UNIVERSITY  OF  CALIFORNIA  PUBLICATIONS 

COLLEGE  OF  AGRICULTURE 

AGRICULTURAL  EXPERIMENT  STATION 

BERKELEY,  CALIFORNIA 


AVOCADO  CULTURE  IN  CALIFORNIA 


PART  I.     History,  Culture,  Varieties,  and  Marketing 

BY 

KNOWLES    RYERSON 


PART  II.     Composition  and  Food  Value 

BY 
M.  E.  JAFFA   AND   H.  GOSS 


BULLETIN  No.  365 

JuxNE,  1923 


UNIVERSITY   OF   CALIFORNIA   PRESS 

BERKELEY,  CALIFORNIA 

1923 


David  P.  Barrows,  President  of  the  University. 

EXPERIMENT  STATION  STAFF 

HEADS  OF  DIVISIONS 

Thomas  Forsyth  Hunt,  Dean. 

E.  J.  Wickson,  Horticulture   (Emeritus). 

,  Director  of  Resident  Instruction. 

C.  M.  Haring,  Veterinary  Science;  Director  of  Agricultural  Experiment  Station. 

B.  H.  Crocheron,  Director  of  Agricultural  Extension. 

C.  B.  Hutchison,  Plant  Breeding;  Director  of  the  Branch  of  the  College  of 

Agriculture  at  Davis. 
H.  J.  Webber,  Sub-tropical  Horticulture;  Director  of  Citrus  Experiment  Station. 
William  A.  Setchell,  Botany. 
Myer  E.  Jaffa,  Nutrition. 
Ralph  E.  Smith,  Plant  Pathology. 
John  W.  Gilmore,  Agronomy. 
Charles  F.  Shaw,  Soil  Technology. 

John  W.  Gregg,  Landscape  Gardening  and  Floriculture. 
Frederic  T.  Bioletti,  Viticulture  and  Fruit  Products. 
Warren  T.  Clarke,  Agricultural  Extension. 
Ernest  B.  Babcock,  Genetics. 
Gordon  H.  True,  Animal  Husbandry. 
James  T.  Barrett,  Plant  Pathology. 
Walter  Mulford,  Forestry. 
W.  P.  Kelley,  Agricultural  Chemistry. 
H.  J.  Quayle,  Entomology. 
Elwood  Mead,  Rural  Institutions. 
H.  S.  Reed,  Plant  Physiology. 
L.  D.  Batchelor,  Orchard  Management. 
W.  L.  Howard,  Pomology. 
fFRANK  Adams,  Irrigation  Investigations. 

C.  L.  Roadhouse,  Dairy  Industry. 
R.  L.  Adams,  Farm  Management. 

W.  B.  Herms,  Entomology  and  Parasitology. 
John  E.  Dougherty,  Poultry  Husbandry. 

D.  R.  Hoagland,  Plant  Nutrition. 
G.  H.  Hart,  Veterinary  Science. 

L.  J.  Fletcher,  Agricultural  Engineering. 
Edwin  C.  Voorhies,  Assistant  to  the  Dean. 


*  In  cooperation  with  Division  of  Agricultural  Engineering,  Bureau  of  Public  Roads,  U. 
Department  of  Agriculture. 


CONTENTS 

PAGE 

Foreword 574 

Part  I.   History,  Culture  Varieties,  and  Marketing 575 

History 575 

Botanical  Descriptions  and  Relations 577 

Avocado  Districts  in  California 580 

Climatic  Requirements 581 

Soils 583 

Orchard  Management 583 

Propagation 583 

Rootstocks 583 

Budding 584 

Topworking 587 

Planting  Systems 592 

Laying  out  the  Orchard 592 

Care  of  Young  Trees 595 

Care  of  Mature  Orchards 596 

Irrigation 596 

Fertilization 599 

Pruning 601 

Harvesting 601 

Frost  Injury  and  Frost  Protection 602 

Wind  Damage 604 

Insect  Pests  and  Diseases 605 

Some  Factors  Affecting  the  Setting  of  Satisfactory  Crops 606 

Pollination , 606 

Bud  Selection 607 

June  Drop 607 

Rootstocks 608 

Girdling 608 

Marketing 609 

Races  and  Varieties 612 

Uses  of  the  Fruit 626 

Yields  and  Returns 627 

Outlook — Present  and  Future 627 

Selected  Reading  List 628 

Acknowledgements 629 

Part  II.   The  Nutritive  Value  of  the  Avocado 630 

The  Average  Composition  of  Fresh  Fruits 630 

Composition  of  the  Avocado 631 

Caloric  Value 636 

Digestibility 637 

Vitamins 637 

Dietetic  Value 638 


FOEEWOED 

The  rapid  growth  of  the  avocado  industry  has  been  one  of  the 
notable  developments  in  California  horticulture  during"  the  past 
decade.  This  period  has  witnessed  a  transition  in  the  use  of  the 
avocado  from  that  of  a  dooryard  curiosity  to  that  of  a  fruit  support- 
ing a  well  established  commercial  industry  embracing  approximately 
a  thousand  acres.  The  first  publication  on  the  avocado  issued  by 
the  College  of  Agriculture  appeared  in  1915  in  response  to  the  need 
expressed  at  that  time.  The  information  then  available  was  neces- 
sarily limited;  the  industry  has  made  rapid  strides  since  its  publica- 
tion ;  methods  and  practices  have  changed ;  and  much  new  information 
has  been  developed.  In  order  to  meet  the  rapidly  growing  demand 
for  the  best  information  available  at  the  present  time,  the  authors 
have  been  requested  to  prepare  this  publication.  The  material 
referring  to  methods,  practices  and  varieties  must  be  considered  in 
relation  to  a  young,  rapidly-growing  industry,  which  has  been  little 
investigated,  hence  the  information  furnished  will  be  subject  to  modi- 
fication as  progress  is  made. 


PART   I 

HISTORY,    CULTURE,    VARIETIES,    AND    MARKETING 

By   KNOWLES  KYEKSON 


HISTORY 

The  first  reference  to  the  introduction  of  the  avocado  into  Cali- 
fornia is  made  in  the  Report  of  the  Visiting  Committee  of  the 
California  State  Agricultural  Society  in  1856.  According  to  this 
report  Dr.  Thomas  J.  White,  living  near  San  Gabriel,  had  imported 
the  avocado  from  Nicaragua  along  with  other  tropical  fruiting  plants. 
It  was  not  until  some  years  later  that  the  avocado  became  definitely 
established  through  the  introduction  of  three  trees  from  Mexico  in 
1871  by  Judge  R.  B.  Ord  of  Santa  Barbara.  Two  of  the  three  trees 
of  his  importation  for  many  years  bore  fruit  in  Santa  Barbara  and 
served  to  create  interest  in  further  plantings. 

California  has  been  fortunate  in  having  had  among  her  early 
settlers  persons  who  have  taken  a  keen  interest  in  horticulture, 
especially  that  phase  of  it  dealing  with  subtropical  plants — fruit- 
bearing  and  ornamental.  The  early  history  of  the  avocado  in  this 
state  is  particularly  marked  by  such  effort.  In  the  years  following 
the  introduction  by  Judge  Ord,  many  trees  were  planted,  some  being 
imported  from  Mexico  and  the  countries  of  Central  America,  others 
being  started  from  the  seeds  of  the  many  fruits  that  had  found  their 
way  into  California,  brought  here  by  travelers.  Among  the  many 
who  contributed  much  to  the  impetus  given  avocado  growing  were 
Mr.  J.  C.  Harvey,  and  Dr.  F.  Franceschi  (Fenzi),  formerly  of  Santa 
Barbara. 

In  the  early  nineties  Mr.  Juan  Murrieta,  becoming  interested  in 
the  avocado  through  Mr.  Harvey,  imported  a  considerable  quantity 
of  thick  skinned  fruits  from  Atlixco,  Mexico.  Some  seeds  from  these 
he  distributed  among  his  friends  and  others  he  planted. '  From  this 
group  of  seedling  trees  have  come  a  number  of  the  varieties  that 
first  attracted  attention,  as  promising  commercial  fruits,  ten  or 
twelve  years  ago.  These  include  the  Royal,  Wa'ker,  Challenge,  Dickey, 
Blakeman,  Sharpless,  Colorado  and  Murrieta.  Mr.  C.  P.  Taft  of 
Orange,  in  1899  and  the  years  immediately  following,  also  planted 
many  seeds  from  various  sources.     As  a  result  of  the  showing  made 


576 


UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 


by  the  fruits  produced  in  the  plantings  mentioned,  interest  in  the 
commercial  possibilities  of  the  avocado  received  a  decided  impetus 
in  1911  and  1912. 

The  period  since,  has  been  marked  by  special  emphasis  on  the 
commercial  aspects  of  avocado  culture  (fig.  1).  In  place  of  relying 
on  chance  seedlings,  nurserymen  began  the  exploration  of  the  avocado 


Fig.  1. — Mature  bearing  avocado  orchard  in  southern  California. 

districts  of  Mexico  and  Guatemala.  F.  0.  Popenoe  and  T.  U.  Barber 
of  the  West  India  Gardens,  Altadena,  were  pioneers  in  this  field,  and 
during  1911-12  brought  in  buds  from  many  varieties  in  the  best 
districts  of  Mexico.  Of  these  the  Fuerte  and  Puebla  have  proved 
to  be  of  especial  merit.  E.  E.  Knight  of  Yorba  Linda,  a  resident  for 
many  years  in  Central  America,  brought  in  buds  of  superior  varieties 
from  Guatemala,  of  which  the  Queen  and  Linda  are  the  most 
promising. 

Mr.  Joseph  Sexton  of  Goleta,  brought  in  selected  seed  and  buds 
from  the  best  West  Indian  varieties  grown  in  the  Hawaiian  Islands. 
The  failure  of  his  planting,  under  favorable  climatic  conditions,  early 
indicated  the  futility  of  planting  varieties  of  this  race.  Realizing, 
however,  that  private  endeavor  could  not  expect  to  cover  completely 


Bulletin  365]  AVOCADO  CULTURE  IN  CALIFORNIA  577 

the  avocado  districts  of  foreign  countries,  and  that  thorough  investi- 
gation should  be  made  in  such  places  if  the  industry  was  to  start 
out  with  the  advantage  of  the  best  varieties  available  as  a  foundation, 
the  U.  S.  Department  of  Agriculture  undertook  the  exploration  of 
all  avocado  districts  in  Mexico  and  Central  and  South  America.  For 
the  better  part  of  nine  years  Wilson  Popenoe,  as  an  agricultural 
explorer,  combed  these  regions,  with  the  result  that  the  avocado 
growers  of  California  and  of  Florida  now  have  the  best  that  the 
world  affords  in  the  way  of  varieties  upon  which  to  build  a  commercial 
industry.  Probably  no  other  horticultural  industry  has  had  a  similar 
advantage  in  its  infancy.  At  the  present  time  these  introductions 
are  being  tested  in  a  number  of  sections  of  southern  California.  It 
will  be  a  matter  of  five  years  at  least  before  their  value  and  adaptation 
to  conditions  in  this  state  will  be  ascertained. 

The  work  of  the  California  Avocado  Association,  which  was 
organized  in  1914,  has  been  one  of  the  important  factors  in  the 
rapid  development  of  avocado  culture.  Its  Committee  on  Registra- 
tion and  Classification  of  Varieties  has  rendered  particular  service 
in  studying  varieties  and  recommending  those  suitable  for  commercial 
planting ;  its  present  list  of  a  few  standard  varieties  is  an  indication 
of  the  careful  work  which  has  characterized  its  activities.  The 
published  proceedings  of  the  organization  form  the  most  valuable 
contribution  to  avocado  literature  available  at  the  present  time. 

BOTANICAL    DESCRIPTIONS    AND    RELATIONS 

The  avocado  belongs  to  the  genus  Persea,  a  member  of  the  Laurel 
family,  to  which  belong  also  such  economic  plants  as  camphor,  sassa- 
fras and  cinnamon.  The  common  native  California  bay  tree  is 
likewise  a  member  of  this  family.  The  cultivated  species  of  this 
genus  are  native  to  Mexico,  Central  and  South  America.  Early 
classification  of  avocados  cultivated  in  the  United  States  placed  all 
in  one  genus,  Persea  americana  Mill.  (P.  gratissima  Gaertn.)  Later 
studies  have  revealed  two  distinct  species,  P.  americana  and  P.  drymi- 
folia;  the  former  includes  all  varieties  horticulturally  grouped  in  the 
West  Indian  and  Guatemalan  races;  the  latter  includes  the  small 
fruited  varieties  of  the  Mexican  highlands,  of  which  many  are  grown 
in  California,  and  have  also  spread  to  Ecuador,  Chile,  and  to  a  limited 
extent  to  the  regions  bordering  the  Mediterranean.  These  are  grouped 
into  the  so-called  Mexican  race. 

P.  drymifolia  can  be  distinguished  from  P.  americana  by  the  very 
pronounced  anise  odor  that  can  be  detected  in  the  leaves  and  young 


578  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

growth  of  the  former  when  crushed,  this  odor  is  entirely  lacking  in 
P.  americana.  The  flowers  of  P.  drymifolia  are  regularly  more  pube- 
scent than  those  of  P.  americana  and  the  under  surface  of  the  leaves 
more  glaucous.  The  fruits  of  P.  drymifolia  are  characterized  by  a 
thin,  membraneous  skin,  differentiating  them  markedly  from  those  of 
P.  americana  which  have  a  thick  skin  varying  from  a  leathery  to  a 
brittle  texture.  The  fruits  of  the  latter  species  are  usually  much 
larger  than  those  of  the  former.  Both  species  are  represented  in  the 
cultivated  avocados  of  California. 

The  tree  is  evergreen,  though  in  certain  varieties  practically  all  of 
the  leaves  drop  for  a  brief  period  during  the  flowering  season.  The 
leaf  blades  are  of  many  different  shapes — oval,  ovate,  obovate,  lance- 
olate, elliptic;  and  combinations  of  these  appear.  The  leaf  base  is 
usually  acute  or  truncate,  the  apex  varies  from  almost  blunt  to 
acuminate.  In  length  the  leaves  vary  from  3  to  15  inches.  The 
color  of  the  mature  foliage  is  usually  bright  green,  the  young  growth, 
however,  often  exhibit  varying  shades  of  red  and  bronze.  The  manner 
of  tree  growth  is  variable,  the  tall,  upright,  unbranched  habit  and 
the  short,  well-shaped,  spreading  habit  are  both  commonly  found. 
Seedling  trees  attaining  an  extreme  height  of  from  fifty  to  sixty 
feet  have  been  noted  where  soil  conditions  are  particularly  favorable 
(fig.  2).  Budding  apparently  has  a  dwarfing  effect.  The  resulting 
trees  are  more  compact  and  spreading,  and  seemingly  not  inclined  to 
grow  as  high  as  seedlings.  None  are  of  sufficient  age  however  to 
settle  this  definitely. 

The  small,  pale,  green  or  yellowish  flowers  are  borne  in  terminal 
racemes.  They  possess  both  stamens  and  pistil.  Differentiation 
between  calyx  and  corolla  does  not  occur  in  the  avocado  blossom. 
The  petal-like  structures  are  in  reality  perianth  lobes,  of  about  equal 
length,  the  inner  series  sometimes  being  longer  than  the  outer.  They 
are  more  or  less  pubescent,  pronouncedly  so  in  P.  drymifolia  and 
sometimes  almost  glaucous  in  P.  americana.  The  nine  stamens  are 
arranged  in  three  series;  the  anthers  are  four-celled,  the  cells  opening 
by  valves  hinged  at  the  upper  end.  At  the  base  of  each  stamen  of 
the  inner  series  are  two  large,  orange  colored  glands  which  secrete 
nectar,  presumably  for  the  attraction  of  insects.  Inside  the  stamens 
are  three  staminoidia.  The  ovary  is  one-celled,  and  contains  a  single 
ovule.  The  style  is  slender,  usually  hairy,  with  a  simple  stigma.  The 
flowers  appear  from  November  to  May  in  California,  varying  accord- 
ing to  variety  and  locality. 


Bulletin  365] 


AVOCADO  CULTURE   IN   CALIFORNIA 


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trees  grow  in  southern  California.    Note  also  the  lath  screen  for  wind  protection. 


580  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

The  fruit  of  the  cultivated  species  is  extremely  variable  in  size, 
shape,  color  and  other  characters.  Fruits  of  P.  drymifolia  are  found 
that  are  no  larger  than  good  sized  olives,  while  the  largest  varieties  of 
P.  americana  weigh  over  three  pounds.  In  shape  they  may  be  round, 
oval,  pyriform,  "bottle  necked,"  or  any  of  the  numerous  gradations 
between  these  forms.  The  color  ranges  from  light,  yellowish  green, 
through  dark  green,  maroon,  brown,  reddish  brown  to  purplish-black. 
The  skin  is  thin  and  membraneous  in  P.  drymifolia,  while  in 
P.  americana  it  is  thick,  tough,  and  even  woody,  or  shell-like  in  some 
varieties,  with  an  extreme  thickness  of  a  quarter  of  an  inch.  The 
fleshy,  edible  part,  lying  between  the  skin  and  the  single  large  seed, 
is  of  a  buttery  consistency,  creamy  to  bright  yellow  in  color,  often 
greenish  near  the  skin.  It  contains  a  high  percentage  of  oil.  Streaks 
of  fine  fibres  traverse  the  flesh  from  the  stem  to  the  base  of  the  seed, 
these  make  up  the  vascular  system,  and  are  invisible  in  ripe  fruits 
of  many  varieties.  Each  fruit  contains  a  single,  large  seed,  and  the 
seeds  of  different  varieties  vary  greatly  in  shape,  being  round,  oblate, 
spherical,  conical,  or  of  slender  form.  The  seed  is  inverted  in  the 
fruit  so  that  the  base  is  on  the  side  away  from  the  stem  and  is 
covered  by  two  seed-coats  of  varying  thickness,  often  adhering  closely 
to  one  another.  The  cotyledons  are  normally  two,  sometimes  three  in 
P.  drymifolia,  white  or  greenish  white  in  color,  and  smooth  or  rough- 
ened on  the  surface.  The  seed  is  tight  in  the  cavity  in  some  varieties 
and  loose  in  others. 


AVOCADO   DISTEICTS    IN    CALIFOENIA 

The  commercial  avocado  plantings  of  the  state  are  located  in 
southern  California  in  two  more  or  less  clearly  defined  districts. 
The  first  is  strictly  coastal,  embracing  Ventura,  Santa  Barbara  and 
parts  of  Orange  and  San  Diego  counties,  and  is  subject  to  direct 
ocean  influence.  The  second  general  district  embraces  the  interior 
foothill  belt  of  San  Fernando  and  San  Gabriel  valleys,  including 
Pasadena,  Monrovia,  Duarte,  through  to  Uplands,  and  on  the  opposite 
side  of  the  valley,  the  North  Whittier  Heights  section.  In  between 
these  two  general  regions  lie  intermediate  districts  such  as  Fillmore, 
Hollywood,  Whittier  and  La  Habra  which  partake  of  the  character- 
istics of  both.  The  plantings  are  for  the  most  part  confined  to  the 
warmer  parts  of  the  citrus  belt.  Plantings  in  the  Coachella  and 
Imperial  Valleys  have  proved  unsuccessful  probably  because  of  the 
extreme  atmospheric  dryness  and  the  intense  heat. 


BULLETIN  365]  AVOCADO  CULTURE  IN  CALIFORNIA  581 

The  avocado  has  been  planted  in  central  and  northern  California 
in  many  scattered  localities.  Trees  are  fruiting  in  Fresno,  Tulare, 
Butte  and  other  counties.  They  are  for  the  most  part  Mexican  seed- 
ling's and  indicate  that  commercial  varieties  may  be  developed  for 
these  sections.  Commercial  plantings  in  these  districts  are  still 
experimental. 

CLIMATIC   REQUIREMENTS 

In  general,  the  avocado  is  similar  to  the  citrus  fruits  in  its  climatic 
requirements.  The  Mexican  race  can  be  grown  where  the  orange 
thrives,  while  the  more  tender  Guatemalan  race  is  adapted  to  the 
milder  districts  best  suited  to  lemon  growing.  Beyond  a  doubt  the 
primary  limiting  factor  of  commercial  avocado  growing  is  the  occur- 
rence of  low  winter  temperatures.  The  relative  importance  of  this 
factor  is  directly  dependent  upon  the  degree  and  duration  of  such 
temperatures.  Observations  made  following  the  cold  waves  of  1913, 
1917  and  1922  have  served  to  verify  these  conclusions.  The  summary 
here  quoted,  made  by  Webber1  following  the  winter  of  1916-1917, 
gives  in  general  the  reactions  of  the  tree  to  the  different  degrees  of 
low  temperature  experienced: 

30  deg.  F. — Nothing  injured  so  far  as  could  be  observed. 

29  deg.  F. — No  injury  of  account;  only  traces  on  most  tender  growth  of 
West  Indian  and  Guatemalan  varieties. 

28  deg.  F. — New  foliage  scorched  on  Guatemalan  types;  West  Indian 
varieties  showing  considerable  foliage  damage. 

27  deg.  F. — Mexican  varieties  showed  new  tips  slightly  scorched;  Guate- 
malans showed  almost  all  new  foliage  injured;  West  Indians  badly 
damaged. 

25  to  26  deg.  F. — Mexican  varieties  showed  new  foliage  injured  but 
some  dormant  trees  uninjured;  all  Guatemalan  sorts  showed  new 
foliage  badly  injured  and  some  old  foliage  scorched. 

24  deg.  F. — Some  dormant  Mexican  varieties  uninjured;  Guatemalan 
varieties  badly  injured,  small  limbs  frozen  back. 

21  deg.  F. — All  Guatemalan  types  killed  to  bud;  a  few  of  the  hardiest 
Mexican  varieties,  such  as  Knowles  and  San  Sebastian,  with  young 
leaves  only  injured. 

Exceptions  occur  due  to  peculiar  local  conditions,  especially  as 
they  affect  individual  tree  vigor.  Varietal  differences  occur  within 
the  two  races  and  will  be  mentioned  later  (fig.  3). 


i  Cold  Eesistance  of  the  Avocado.    H.  J.  Webber,  Annual  Report,  California 
Avocado  Association,  1917,  p.  49. 


582 


UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 


The  avocado  is  also  sensitive  to  hot  summer  temperatures.  This 
factor  is  the  main  reason  for  its  failure  in  the  hot,  dry,  interior 
sections.  Intense  heat  waves  in  the  more  favorable  districts  have 
caused  serious  damage  in  the  past.  Two  varieties,  the  Caliente  and 
the  Tiger,  have  shown  some  promise  of  heat  resistance  in  the  more 
arid  districts. 


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Fig.  3. — Eelative  frost  resistance  of  seedling  avocado  trees  of  Guatemalan 
and  Mexican  origin.  They  were  located  in  an  exposed  section  of  the  San  Gabriel 
Valley  with  no  frost  protection.     Injury  caused  by  cold  wave  of  January,  1922. 


Atmospheric  humidity  is  a  factor  of  importance  as  evidenced  by 
the  behavior  of  the  avocado  in  different  parts  of  the  state.  The  tree 
thrives  best  in  the  more  humid  coastal  districts.  Dry  atmospheric 
conditions  are  detrimental  as  evidenced  by  the  failure  of  trees  to 
succeed  in  the  Coachella  and  Imperial  Valleys. 

Since  avocado  culture  is  carried  on  in  California  entirely  under 
irrigation,  the  question  of  rainfall  is  not  of  importance  except  as  it 
insures  an  adequate  supply  of  irrigation  water. 

Wind  has  an  important  influence  in  avocado  culture  and  is  dis- 
cussed in  another  section. 


Bulletin  365]  AVOCADO  CULTURE  IN  CALIFORNIA  583 

SOILS 

Observations  on  the  behavior  of  the  avocado  in  California  indicate 
that  it  thrives  on  a  wide  range  of  soils.  Commercial  plantings  are 
found  on  the  very  light,  sandy  soils  and  on  the  heavy  black  adobes 
and  on  the  many  different  types  between  these  two  extremes.  It 
seems  to  do  best,  however,  on  the  medium  textured  soils.  For  satis- 
factory results  a  depth  of  at  least  four  feet  is  recommended.  The 
avocado  is  extremely  sensitive  to  poor  drainage  and  will  not  endure 
a  saturated  soil  for  more  than  a  few  days. 

In  selecting  planting  sites,  the  slope  and  character  of  the  sub- 
soil are  the  most  important  soil  factors  to  investigate.  Hardpan  layers 
close  to  the  surface  are  unfavorable  and  should  be  avoided. 

ORCHAED  MANAGEMENT 
Propagation 

Rootstocks. — Experience  in  handling  and  growing  budded  avocado 
trees  during  the  past  few  years  has  pointed  out  the  necessity  of 
giving  more  careful  attention  to  the  rootstock  upon  which  the  tree 
is  grown.  In  the  beginning  any  kind  of  seed  procurable  was  used 
to  raise  seedlings — West  Indian,  Guatemalan,  Mexican — large,  small', 
mature  and  immature — with  the  result  that  many  nursery  trees  failed 
to  make  satisfactory  growth  and  great  numbers  died.  The  West 
Indian  seedlings  have  proved  unsatisfactory  because  of  their  tender- 
ness, and  their  use  has  been  entirely  abandoned.  The  use  of  Guate- 
malan seedlings  as  rootstocks  has  been  largely  discontinued  for  the 
same  reason.  The  seed  of  the  small,  thin-skinned  Mexican  race  is  now 
being  used  almost  exclusively,  and  the  results  have  warranted  strict 
adherence  to  this  practice.  There  is  a  wide  variation  within  the 
Mexican  race,  in  both  thrift  and  vigor;  seed  from  mature,  well- 
developed,  and  well-shaped  fruit  only  should  be  used.  Because  of  the 
great  variation  in  size  and  vigor  of  Mexican  seedlings,  it  is  believed 
that  many  of  the  fruits  have  resulted  from  crossing  with  large-fruited 
Guatemalans  growing  in  the  vicinity,  and  that  the  resultant  seedlings 
are  in  reality  hybrids  with  all  the  opportunity  for  variation  that  such 
a  condition  affords.  There  is  reason  to  believe  that  variation  and  lack 
of  congeniality  from  this  cause  would  be  minimized  should  only  that 
seed  be  used  which  is  known  to  come  from  flowers  pollenized  by  other 
Mexican  trees. 

Several  methods  are  used  in  starting  seeds,  differing  only  in  minor 
details.  Seeds  are  usually  planted  in  boxes  containing  at  least  six 
inches  of  a  mixture  of  loam  and  clear  sand,  a  mixture  of  half  of  each 


584  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

being  a  common  practice.  The  seeds  are  planted  base  downward  with 
about  a  half  inch  of  the  apex  protruding  above  the  soil.  Large  beds 
are  sometimes  made  either  over  a  hotbed  or  in  the  open.  Muslin  or 
lath  screens  are  placed  over  the  beds  during  the  hottest  part  of  the 
day  during  hot  weather.  It  was  formerly  a  rather  common  method 
to  plant  the  seeds  in  four-inch  pots,  but  this  practice  has  for  the 
most  part  been  discontinued.  They  are  best  planted  as  soon  as  possible 
after  removal  from  the  fruit,  but  may  be  kept  several  months  if  not 
permitted  to  dry  out.  Since  most  of  the  Mexican  varieties  ripen  in 
late  summer  and  fall,  seed  is  usually  planted  during  this  time  of  the 
year.  Growth  starts  in  late  winter  or  early  spring,  so  that  the  seed- 
lings are  ready  to  be  set  out  in  April  when  they  have  attained  a 
height  of  four  to  six  inches. 

When  danger  of  frost  is  over  and  the  seedlings  have  reached  the 
height  mentioned,  they  are  usually  transplanted  directly  to  the  nursery 
rows,  fourteen  to  eighteen  inches  apart  in  the  row,  and  the  rows  forty 
inches  to  four  feet  apart.  Irrigation  should  immediately  follow  plant- 
ing to  prevent  drying  out.  If  the  weather  is  particularly  warm, 
temporary  protection  from  the  sun  is  necessary  and  is  usually  provided 
by  placing  a  shingle  on  the  south  side  of  each  seedling.  Some  nursery- 
men have  in  the  past  planted  the  seedlings  in  four-inch  pots,  later 
setting  them  out  in  the  field  from  the  pots  before  or  after  budding. 
Because  of  danger  of  the  curling  of  the  roots  at  the  bottom  of  the 
pot,  which  may  result  in  permanent  injury,  this  practice  has  been 
discontinued.  It  can  be  used  with  safety  where  the  seedlings  are 
only  held  from  three  to  four  weeks  before  transplanting.  Frequent 
watering  is  necessary  until  they  become  established,  after  which 
irrigation  every  two  weeks  should  be  sufficient  excepting  in  extremely 
hot  weather. 

Budding. — The  operation  of  budding  is  simple,  but  must  be  carried 
out  with  unusual  care  and  attention  in  every  detail  to  insure  success. 
Most  of  the  failures  common  to  the  beginner  are  directly  traceable 
to  the  neglect  of  some  detail.  The  selection  of  bud-wood  must  be 
made  with  unusual  care  and  with  a  knowledge  of  the  peculiarities 
of  each  variety. 

Seedlings  to  be  used  for  budding  should  be  kept  in  a  thrifty, 
growing  condition.  They  may  be  budded  any  time  during  the  season 
when  the  sap  is  flowing  freely,  after  they  have  attained  a  diameter 
slightly  larger  than  that  of  a  lead  pencil.  Usually  this  begins  early 
in  the  spring,  with  April  and  May  very  good  months  for  the  operation. 
For  budding  during  these  months,  well  matured  wood  from  the 
previous  season's  growth  may  be  used.     After   active  growth  has 


Bulletin  365]  AVOCADO  CULTURE  IN  CALIFORNIA 


585 


Fig.  4. — Desirable  types  of  budwood  used  in  the  propagation  of  avocado  trees. 


586  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

commenced,  suitable  buds. are  not  available  until  the  new  growth  has 
hardened,  usually  by  the  latter  part  of  June.  From  this  time  budding 
can  again  be  commenced  and  continued  until  late  in  the  fall.  A 
certain  percentage  of  the  buds  inserted  in  the  fall  will  push  out  and 
make  some  growth  and  will  require  extra  protection  during  the  winter. 
Only  buds  put  in  very  late  in  the  fall  can  be  counted  on  to  remain 
dormant  until  spring. 

Ordinarily  wood  that  is  well  matured  with  fairly  plump  buds, 
that  is  not  hard  and  yet  does  not  snap  on  bending,  furnishes  the  best 
material  for  buds  (fig.  4).  Varieties  like  the  Spinks  and  the  Fuerte 
will  give  high  percentage  stands  from  young  buds  taken  almost  to 
the  tip  of  young  growth.  Intimate  knowledge  of  the  peculiarities  of 
each  variety  comes  only  with  practice  and  observation. 

Shield  budding,  such  as  is  used  in  the  propagation  of  citrus  and 
deciduous  fruits,  is  the  common  nursery  practice.  A  "T"  incision 
is  made  within  two  or  three  inches  of  the  ground,  preferably  on  the 
north  side  of  the  seedling.  The  bud  is  cut  with  a  shield  not  less 
than  an  inch  and  a  quarter  in  length,  and  is  pushed  gently  into  the 
incision.  The  stock  should  be  in  such  condition  of  growth  that  the 
bark  will  slip  readily,  and  will  not  require  lifting  by  the  knife  blade, 
otherwise  it  is  too  dry  to  be  used  successfully. 

The  knife  blade  used  for  cutting  buds  should  be  thin  and  should 
be  kept  with  a  razor  edge.  The  cut  should  be  made  parallel  to  the 
surface  of  the  stick  with  a  single  sliding  motion ;  much  of  the  success 
of  budding  depends  on  having  the  cut  uniform,  smooth  and  straight. 

After  insertion,  the  bud  is  immediately  wrapped,  beginning  at 
the  top  and  working  down.  Various  materials  are  used ;  raffia,  cotton 
twine,  rubber  bands,  muslin,  and  budding  cloth,  all  are  employed. 
Budding  cloth  is  recommended,  provided  a  hard  wax  is  used  in  its 
manufacture  which  will  not  melt  and  injure  the  bud  in  hot  weather. 
A  wax  composed  of  one  pound  of  beeswax  and  one  quarter  of  a  pound 
of  rosin  is  satisfactory.  Cheap  grades  of  muslin  are  made  up  into 
rolls  six  inches  wide  and  one  inch  in  diameter,  and  boiled  in  the  wax 
for  fifteen  minutes. 

About  three  weeks  are  required  for  the  buds  to  unite  with  the 
stock,  during  which  period  they  should  be  examined  and  the  wraps 
loosened  to  prevent  binding.  The  top  should  be  pinched  back  at  this 
time  in  order  to  start  the  bud  into  growth.  From  six  to  eight  weeks 
after  budding  the  wraps  may  be  safely  removed.  After  another  month 
of  growth  the  seedling  should  be  cut  back  still  further,  leaving  some 
foliage  to  take  care  of  the  sap  flow.  When  the  bud  has  made  a 
growth  of  four  to  six  inches  it  should  be  tied  up  to  the  stock  with 


Bulletin  365]  AVOCADO  CULTURE  IN  CALIFORNIA  587 

raffia ;  staking  should  be  done  when  it  has  reached  a  height  of  sixteen 
to  eighteen  inches.  The  seedling  top  should  not  be  cut  off  until  the 
bud  has  grown  at  least  two  feet ;  this  operation  is  best  done  when 
the  top  has  become  somewhat  hardened.  A  sloping,  smooth  cut  close 
to  the  bud  union  should  be  made  and  the  wound  painted  over  with 
grafting  wax. 

A  novel  adaptation  of  budding  has  been  developed  by  A.  R. 
Rideout,  of  Whittier,  in  an  effort  to  obtain  an  earlier  indication  of  the 
results  of  seed  selection.  Seeds  are  sprouted  in  the  regular  way. 
When  the  rootlets  are  about  an  inch  long,  one  of  the  two  halves  of  the 
seed  is  carefully  removed  without  disturbing  the  developing  plantlet. 
A  sharp  cut  is  made,  beginning  at  the  base  of  the  tiny  shoot  and 
extending  through  to  the  root  tip.  The  other  half  of  the  seed  is 
sometimes  cut  away,  leaving  a  small  wedge-shaped  portion  to  assist 
in  forcing  the  rootlet  into  the  incision,  or  it  may  be  left  on  entirely. 
The  sprouting  seeds  so  prepared  are  then  inserted  in  limbs  of  mature 
trees  or  on  nursery  stocks  by  means  of  long  (<T"  incisions.  The  tip 
of  the  root  is  inserted  at  the  intersection  of  the  horizontal  and  vertical 
incisions  and  gently  forced  down  in  the  same  manner  as  in  shield 
budding,  until  the  split  radical  is  well  in  place.  Strips  of  specially 
prepared  budding  rubber  an  eighth  of  an  inch  in  width  are  used  to 
bind  the  sprouted  embryo  in  place  and  a  piece  of  dentist's  rubber 
sheeting  is  wrapped  over  the  area  to  prevent  drying  out  and  to 
exclude  the  entrance  of  water  from  without  until  union  has  taken 
place.  By  this  method  the  seedling  becomes  a  new  branch  on  a  mature 
tree  or  the  top  of  a  young  tree,  and  probably  will  come  into  fruiting 
considerably  sooner  than  if  grown  as  a  seedling  plant.  The  operation 
is  not  at  all  difficult  and  requires  only  skill  on  the  part  of  the  operator. 

Field  grown  trees  are  best  balled  prior  to  the  early  spring  growth. 
They  may  be  taken  up  any  time  during  December,  January  and 
February,  and  even  in  March  when  the  season  is  late.  A  ball  of 
earth  ten  to  twelve  inches  in  diameter  and  fourteen  to  eighteen  inches 
in  length  is  removed  with  each  tree,  depending  upon  age  and  vigor 
of  growth  (fig.  5) .  The  trees  should  be  cut  back  partially,  or  partially 
defoliated,  or  both,  to  balance  the  loss  of  part  of  the  root  system, 
and  should  be  kept  under  lath  and  well  watered  from  four  to  six 
weeks,  until  they  become  hardened. 

Some  experiments  have  been  tried  planting  budded  avocados  with 
bare  roots,  but  these  have  not  been  very  successful,  and  the  practice 
cannot  be  recommended. 

Topworking. — The  occurrence  of  many  unproductive  trees  and 
trees  producing  inferior  types  of  fruit  has  created  much  interest  in 


588  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

methods  of  working  them  over  to  desirable  productive  strains.  Several 
successful  methods  have  been  developed;  of  these,  budding  and  cleft 
grafting  are  the  most  generally  used.  In  budding  over  large  trees, 
buds  are  inserted  directly  into  the  old  bark  on  the  trunk  or  main 
limbs  wherever  possible  in  order  to  save  time  and  to  form  the  new 
top  close  to  the  head. 

From  one-third  to  one-half  of  the  top  is  first  removed  by  a  thinning 
out  pruning.  The  trunk  and  limbs  exposed  should  be  given  a  coat 
of  whitewash  to  prevent  sunburn.  From  two  to  four  buds  are  inserted 
in  each  of  the  branches  to  be  budded  in  such  a  manner  that  one  wrap- 
ping suffices  for  all.  One  or  two  ' '  safety ' '  limbs  are  generally  left  to 
nourish  the  roots  and  take  the  surplus  sap  until  the  new  head  is 
established,  after  which  they  are  removed. 

Buds  are  taken  from  mature  wood  one-half  to  one  inch  in  diameter. 
They  are  cut  to  a  length  of  about  two  inches,  the  upper  or  lower  end 
being  cut  off  square  to  facilitate  forcing  the  bud  into  the  incision, 
according  to  whether  the  ordinary  "T"  or  inverted  "T"  incision  is 
used.  Where  the  bark  is  very  thick  it  is  scraped  as  an  aid  to  easy 
insertion.  The  wrapping  commonly  used  is  No.  16  white  cotton  string ; 
it  is  wound  tightly  over  the  bud,  leaving  only  the  eye  exposed.  This 
wrapping  should  be  left  on  for  at  least  two  months,  since  if  cut  earlier 
the  bark  on  large  trees  has  a  tendency  to  lift  away  from  the  bud. 
Sucker  growths  are  removed  in  order  to  start  the  buds  into  growth. 
The  new  buds  are  carefully  tied  to  the  limbs  to  prevent  breaking. 
The  budded  limb  should  not  be  cut  back  until  the  new  growth  has 
become  somewhat  hardened  and  is  able  to  take  care  of  the  sap  flow ; 
this  operation  is  usually  done  the  following  season.  It  may  be 
necessary  to  pinch  back  the  bud  shoots  to  encourage  early  branching. 

Considerable  time  can  be  saved  if  cleft-grafting  is  used  instead 
of  budding.  The  drawback  to  this  method  is  the  increased  cost  of 
scions.  Fewer  can  be  taken  from  any  one  tree  because  of  the  excessive 
amount  of  cutting  back  required  to  secure  them.  Where  trees  have 
well-formed  heads  consisting  of  two  or  three  well-spaced  framework 
limbs,  a  new  head  can  be  built  by  inserting  two  scions  in  each, 
eventually  removing  one  of  the  scions  if  both  take,  leaving  the  more 
vigorous.  Limbs  not  used  for  grafting  are  gradually  removed  as  the 
new  top  develops  and  is  able  to  take  care  of  the  entire  sap  flow.  Very 
large  trees  with  no  branches  close  to  the  ground  can  be  successfully 
reworked  by  cutting  off  the  trunk  at  a  height  of  about  four  feet 
and  inserting  at  least  four  scions.  Special  precautions  must  be  taken 
to  keep  large  wounds  well  protected  against  the  entrance  of  heart 
rot  fungi  by  the  use  of  waterproof  paint  or  wax. 


BULLETIN  365]  AVOCADO  CULTURE  IN  CALIFORNIA 


589 


Fig.  5. — Year  old  budded  nursery  stock,  balled  ready  for  shipment. 


590  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

Avocado  wood  is  unusually  brittle  and  in  sawing  off  limbs  to  be 
grafted  the  first  cut  should  be  made  about  a  foot  or  more  above  the 
point  where  the  scions  are  to  be  inserted.  This  is  done  to  prevent 
splitting,  and  permits  the  second  cut  to  be  made  clean  and  smooth. 
The  scions  should  be  of  second  growth  wood,  well  matured,  and  should 
have  two  or  three  buds  well  placed,  plump  and  well  formed,  but  not 
far  advanced.  It  is  especially  desirable  for  the  scion  to  include  a 
growth  made  near  the  base  so  that  advantage  may  be  taken  of  the 
many  adventitious  buds  arising  in  that  zone.  This  insures  growth, 
once  union  is  effected.  The  scions  are  cut  wedge-shaped,  tapering 
for  a  distance  of  one  and  a  half  to  two  inches,  depending  somewhat 
upon  the  size  of  the  wood  used  and  the  limbs  to  be  grafted.  The 
cuts  are  also  tapered  slightly  from  front  to  back,  giving  a  very  slight 
wedge  shape,  enabling  the  scion  to  fit  more  closely  into  the  cleft. 
Much  of  the  success  in  topworking  depends  upon  making  the  cuts 
smooth  and  even,  and  the  knife  used  for  this  purpose  should  be  kept 
at  razor  sharpness  by  means  of  frequent  stropping. 

The  cleft  is  made  with  an  ordinary  butcher 's  cleaver,  care  being 
taken  to  split  the  limb  some  distance  beyond  that  required  by  the 
length  of  the  scions.  This  reduces  the  pressure  exerted  on  them.  The 
edges  of  the  cleft  should  be  trimmed  smooth  with  a  knife.  A  hard- 
wood wedge  is  driven  into  the  center  of  the  cleft  and  the  scions  fitted 
so  that  the  cambium  layer  of  the  scion  and  that  of  the  stock  coincide 
as  closely  as  possible  throughout  their  entire  length.  The  wedge  is 
then  removed  and  budding  cloth  strips  half  an  inch  in  width  are 
wrapped  tightly  around  the  end  of  the  limb.  Grafting  wax  is  painted 
over  the  surface  of  the  cuts  and  poured  down  into  the  cleft  so  as  to 
fill  it.  The  tops  of  the  scions  are  tipped  with  wax.  Where  the  bark 
is  thick,  necessitating  the  setting  in  of  the  scions,  the  space  between 
the  bark  and  the  scions  is  also  filled  with  wax  before  the  budding 
cloth  wrapping  is  applied.  A  good  wax  may  be  made  up  of  three 
parts  of  rosin  and  one  of  beeswax.  The  operation  is  completed  by 
placing  a  paper  bag  over  the  end  of  the  limb,  cutting  a  small  hole  for 
ventilation.  This  is  not  removed  until  they  have  made  a  good  start. 
The  trunk  and  branches  should  be  protected  again  sunburn,  preferably 
by  whitewashing    (fig.   6). 

The  follow-up  work  is  of  especial  importance.  Rewaxing  is  usually 
necessary  to  prevent  drying  out.  Supports  should  be  provided  early 
to  hold  up  the  rapidly  growing  shoots.  These  are  best  supplied  by 
tying  two-inch  pieces  to  the  limbs  on  which  the  scions  are  located; 
this  allows  flexibility  and  at  the  same  time  sufficient  rigidity  to  insure 
adequate  support.     These  supports  will  need  to  be  lengthened  from 


Bulletin  365] 


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591 


time  to  time,  even  after  the  growth  is  six  to  eight  feet  high,  until  it 
is  well  hardened.  The  best  time  for  cleft  grafting  is  February  to 
May,  depending  upon  the  season  and  the  ability  to  get  scion  material. 
This  method  has  the  advantage  that  if  the  scions  fail  to  grow  the 
new  shoots  arising  below  the  cuts  can  be  budded  a  few  months  later. 


Fig.  6. — Avocado  tree  topworked  by  cleft  grafting.     Note  the  nurse  limbs 
left,  Mhitewashed  trunk  and  branches,  and  paper  bag  protectors. 

Other  methods  of  topworking  which  have  been  used  with  success 
are  bark  grafting  and  side  grafting.  In  the  former  the  limb  or  trunk 
is  cut  off  square,  and  the  incisions  are  made  from  this  point  down- 
ward for  a  distance  of  about  two  inches  (fig.  7)  ;  in  the  latter  the 
regular  vertical  ' l  T ' '  incision  used  in  budding  is  made  on  the  side  of 
the  limb  or  trunk  (fig.  8).  Cutting  back  is  done  after  the  scions  have 
developed.  The  scions  are  selected  from  well  matured  wood  and  made 
with  a  long  sloping  cut  on  one  side  only.  They  are  pushed  down  into 
the  incision  after  the  manner  of  budding.  Tying,  waxing  and 
follow-up  work  are  the  same  as  for  the  other  methods.     These  two 


592 


UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 


types  of  grafting  are  best  done  in  the  active  growing  season  during 
the  summer  months,  as  success  depends  on  the  easy  lifting  of  the  bark. 
Seedlings  and  named  varieties  exhibit  a  wide  variation  in  the  ease 
with  which  they  may  be  worked  over  to  some  other  desired  variety. 
The  Taft  seems  particularly  difficult  to  top  work  by  cleft  grafting ; 
some  others  behave  in  a  similar  manner.  The  congeniality  between 
the  tree  to  be  topworked  and  the  desired  variety  from  which  scions 
will  be  taken  should  be  learned  if  possible  before  attempting  the 
operation.  >  j!  >  j 


Wj 

H       4 

Fig.  7. — Bark  grafted  qvocado  limb.  The  cut  surface  should  be  well  pro- 
tected by  a  waterproof  coating. 

Planting  Systems 

Laying  Out  the  Orchard. — Two  general  systems  of  planting  are 
in  use:  the  square  system,  adapted  to  the  gently  sloping  and  more 
level  lands,  and  the  system  of  terrace  planting  used  on  the  steeper 
hill  slopes.  In  the  ordinary  square  system  planting  distances  vary 
from  15  x  15  feet  to  30  x  30  feet,  according  to  variety.  The  tall, 
upright-growing  Lyon  is  being  set  at  the  minimum  distance  given, 
while  the  Fuerte,  Spinks  and  similar  strong  growing  varieties  are 
being  planted  from  24  to  30  feet  apart,  with  a  preference  for  the 
latter  distance.  With  certain  varieties,  under  favorable  conditions 
of  soil  and  climate,  this  distance  may  have  to  be  increased  as  more 
is  learned  about  the  growth  of  the  budded  avocado  tree. 


Bulletin  365]  AVOCADO  CULTURE  IN  CALIFORNIA  593 

In  recent  years  the  development  of  hillside  lands  for  avocado 
plantings  has  come  into  considerable  prominance.  On  account  of 
the  protection  from  frost  afforded  by  the  elevation,  extensive  hillside 
planting's  have  been  made,  especially  in  the  North  Whittier  Heights, 
La  Habra  and  Whittier  districts  (fig.  9).  This  system  is  of  course 
more  expensive  because  of  the  greatly  increased  cost  of  laying  out 
the  orchard  and  the  higher  costs  of  orchard  management.  The  limit 
of  the  steepness  of  the  slope  beyond  which  it  is  not  practicable  to 


Fig.  8. — Side  grafting  of  the  avocado.     This  method  can  be  used  any  time 
when  the  bark  slips  readily. 

terrace  is  estimated  to  be  about  30  degrees.  The  contour  grade  varies 
from  1  to  2y2%,  according  to  the  distance  the  irrigation  water  will 
have  to  flow.  The  width  of  the  terraces  varies  from  seven  to  sixteen 
feet,  the  latter  distance  being  considered  the  better  when  the  slope 
permits.  With  narrow  terraces  nearly  all  cultivation  must  be  done 
by  hand.  The  trees  are  planted  two  to  five  feet  inside  the  edge  of  the 
terrace,  the  tendency  at  the  present  time  being  to  plant  them  in 
far  enough  so  that  irrigation  furrows  may  be  run  on  both  sides.  The 
cost  of  terracing  hillside  land  varies  from  $100  to  $150  per  acre, 
according  to  the  steepness  of  the  slope  and  the  character  of  the  soil. 


594 


UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 


Where  possible  grading  should  be  done  so  that  winter  rains  can  have 
the  opportunity  of  settling  the  terraces  and  indicating  any  irregu- 
larities that  may  interfere  with  the  flow  of  irrigation  water.  It  is 
advisable  to  run  water  down  each  terrace  as  a  final  test  before  putting 
in  the  trees ;  changes  in  the  terraces  are  difficult  to  make  after  planting 
has  been  done.  The  distance  terraces  are  placed  apart  averages  about 
thirty  feet,  varying  according  to  the  slope  and  contour  of  the  hillside. 
They  may  be  brought  closer  together  or  spread  wider  apart,  necessi- 
tating the  elimination  of  some  of  the  planting,  or  the  addition  of  short 


Fig.  9. — Construction  of  terraces  for  an  avocado   orchard  near  La  Habra, 
California.      (Photo  by  Webber.) 

rows  in  between  to  insure  filling  the  entire  space.  Special  care  is 
necessary  during  the  rainy  season  to  prevent  excessive  erosion.  Ade- 
quate surface  drainage  must  be  provided.  The  control  of  weeds  is 
more  difficult  on  terraced  plantings,  because  of  the  banks  between 
terraces  which  can  not  be  handled  by  horse  or  tractor  drawn  imple- 
ments. Trees  are  planted  15  to  40  feet  apart  on  the  terraces,  accord- 
ing to  variety. 

On  both  terraced  and  level  plantings  considerable  attention  has 
been  devoted  to  the  interplanting  of  different  varieties  with  the  idea 
of  removing  a  portion  of  the  trees  when  they  reach  maturity.  For 
this  purpose  varieties  for  interplanting  should  have  either  an  upright, 
slender  habit  of  growth  or  early  bearing  qualities,  characteristics 
especially  prominent  in  the  Lyon,  which  is  being  used  for  this  purpose. 
Interplanting  has  much  to  commend  it  and  will  doubtless  increase. 


Bulletin  365] 


AVOCADO  CULTURE   IN   CALIFORNIA 


595 


The  practice  of  replacing  diseased  or  decadent  citrus  trees  by 
avocados  is  on  the  increase  and  bids  fair  to  become  an  important 
method  of  establishing  avocado  orchards,  especially  in  the  old  citrus 
districts.  By  this  means  some  income  from  the  citrus  orchard  is 
received  while  the  avocado  trees  are  coming  into  bearing.  The  leveling 
and  irrigation  system  are  provided  for,  and  the  citrus  trees  offer 
considerable  protection  to  the  young  avocado  trees.  Thus  far  the 
avocado  seems  to  be  practically  immune  to  the  attacks  of  gophers.  The 
method  is  being  watched  with  interest. 


Fig.  10. — The  furrow  system  of  irrigation  is  commonly  used  on  terraces. 
The  length  of  the  furrows  should  not  exceed  three  hundred  feet. 

There  is  at  least  one  possible  drawback  to  this  method.  The  pollin- 
ation of  those  varieties,  the  blooming  period  of  which  coincides  with 
that  of  citrus  trees,  would  possibly  suffer  from  the  fact  that  bees 
seem  to  prefer  citrus  flowers.  Placing  additional  hives  in  the  orchard 
may  overcome  the  difficulty.     Definite  information  on  this  point  is 

lacking. 

Care  of  Young  Trees 

Nursery  trees  set  out  in  the  orchard  require  special  attention 
during  their  early  life  if  they  are  to  make  satisfactory  orchard  trees. 
They  should  be  planted  in  large  holes  at  least  two  feet  in  diameter 
and  three  feet  deep  and  top  soil  should  be  used  to  fill  in.    The  use  of 


596  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

manure  and  fertilizers  when  planting:  is  not  advisable  for  reasons  dis- 
cussed later.  Young  trees  should  never  lack  water;  they  should  be 
irrigated  immediately  after  setting  and  frequently  thereafter  until 
well  established,  after  which  irrigation  at  ten-day  or  two-week  inter- 
vals should  ordinarily  be  sufficient. 

Adequate  protection  from  sunburn  is  of  especial  importance.  If 
set  out  during  the  cool  weather  in  early  spring,  trees  may  become 
established  without  the  use  of  special  sunshades,  but  their  use  is 
recommended.  The  trunks  should  be  given  a  coat  of  whitewash  and 
the  trees  staked. 

Cultivation  to  prevent  the  soil  becoming  packed  around  the  young 
trees,  and  to  keep  down  weeds,  is  essential.  The  surface  soil  should  be 
maintained  in  optimum  condition  to  take  water  readily.  Some  growers 
have  found  it  a  good  practice  to  make  basins  and  mulch  the  surface 
around  young  trees  with  bean  straw  or  alfalfa  straw.  This  practice 
appears  to  be  especially  effective  where  the  soil  in  the  ball  is  heavier 
in  texture  than  the  soil  in  which  the  young  tree  is  set. 

Care  of  Mature  Orchards 

Cultural  operations  in  mature  avocado  orchards  differ  little  if  any 
from  those  practiced  in  citrus  orchards.  Spring  plowing  or  disking 
and  summer  cultivation  is  usually  practiced.  Cultural  operations 
should  be  designed  primarily  to  maintain  conditions  favorable  to  the 
penetration  of  irrigation  water.  Weeds  should  be  kept  down.  On 
terraced  plantings,  plowing  one  way  in  the  spring  is  about  all  that 
can  be  done,  and  on  narrow  terraces  is  accomplished  with  difficulty, 
if  at  all.  As  the  trees  spread  out  and  cover  such  terraces  the  point 
is  reached  when  hand  work  alone  must  be  relied  on. 

Since  the  avocado  is  by  nature  a  shallow  rooted  tree,  abrupt 
changes  in  depth  of  plowing,  or  cultivating,  are  not  recommended. 

IRRIGATION 
In  general  the  water  requirement  of  avocado  trees  is  similar  to 
that  of  citrus  trees.  Both  are  native  to  regions  of  high  rainfall  which 
comes  during  the  growing  season.  The  root  system  of  the  avocado 
is  also  similar  to  that  of  the  citrus  trees,  the  feeding  rootlets  being 
fibrous  and  located  for  the  most  part  in  the  upper  four  feet  of  soil. 
For  proper  growth  and  productivity  the  avocado  tree  requires  a 
uniform  moisture  condition  in  the  soil  throughout  the  entire  root  zone, 
during  all  of  the  growing  season.  Many  observations  indicate  that 
on  all  but  the  heaviest  soils  this  condition  is  best  maintained  by  more 
frequent  and  more  generous  applications  of  water  than  have  been 
given  in  the  past. 


Bulletin  365] 


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597 


The  amount  of  water  required  annually  is  equivalent  to  a  rainfall 
of  thirty-five  to  forty  inches.  Since  the  annual  rainfall  in  the  avocado 
districts  seldom  exceeds  twenty  inches,  approximately  an  equal 
amount  must  be  applied  in  the  form  of  irrigation,  or  at  the  rate  of 
three  to  four  acre  inches2  per  month  during  the  five  or  six  dry  months. 


Fig.  11. — Special  equipment  has  been  developed  for  irrigating  hillside  plant- 
ings. The  above  distributor  is  used  where  the  pipeline  passes  down  a  ridge 
with  the  furrows  sloping  each  way  from  it.  It  is  jointed  so  that  it  can  be  raised 
vertically  to  be  out  of  the  way  of  cultural  operations. 


There  is  some  evidence  that,  with  the  possible  exception  of  the  heavier 
soils,  the  monthly  period  between  irrigations  is  too  long  and  that  an 
interval  of  two  to  three  weeks  is  much  more  desirable.     The  only 

2  An  acre  inch  is  approximately  equivalent  to  the  flow  of  1  miner's  inch  of 
water  in  50  hours  or,  conversely,  50  miner's  inches  flowing  for  1  hour  on  1  acre, 


598  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

satisfactory  way  to  determine  moisture  conditions  is  to  examine  the 
soil  to  a  depth  of  at  least  four  feet.  This  can  be  done  to  best  advantage 
in  most  soils  with  a  soil  auger,  or  post  hole  auger.  This  should  be  a 
regular  orchard  practice. 

Methods  of  applying  irrigation  water  to  avocado  orchards  vary. 
The  prevalent  practice  is  the  use  of  furrows;  this  method  gives 
satisfaction  where  the  slope  is  not  too  steep  and  the  soil  not  so  porous 
as  to  result  in  loss  of  moisture  and  plant  food  by  excessive  pene- 
tration. For  terrace  plantings  (fig.  10),  furrows  should  not  exceed 
three  hundred  feet  in  length  (fig.  11),  for  ordinary  conditions,  fur- 
rows anywhere  from  three  hundred  to  four  hundred  feet  in  length 
are  most  satisfactory.  The  use  of  cross  furrows  to  supply  water  in 
the  dry  portions  of  the  tree  rows  is  recommended. 

The  mulched  basin  system  has  been  tried  with  varying  success. 
Poorly  drained  basins  in  heavy  soils  have  been  known  to  cause  the 
death  of  trees  from  suffocation  during  the  rainy  season.  Opinions 
differ  in  regard  to  the  ultimate  success  of  this  system.  Some  growers 
have  already  discontinued  its  use,  while  others  continue  it  in  new 
plantings.  It  reduces  the  amount  of  cultivation,  is  conducive  to 
the  maintenance  of  uniform  soil  moisture  and  temperature  condi- 
tions, and  supplies  organic  matter  to  the  soil — where  sufficient 
mulching  material  is  kept  in  the  basins.  However,  the  basins  are 
rather  costly  to  install  on  very  steep  slopes  and  are  expensive  to 
maintain. 

On  the  lighter  soils  flooding  is  necessary  to  get  the  water  evenly 
distributed  over  the  entire  area,  since  a  sufficient  head  can  not  be 
maintained  to   carry  the  water  down  furrows. 

Much  attention  is  being  devoted  to  overhead  sprinkling  systems 
in  avocado  plantings,  following  the  example  of  some  of  the  citrus 
growers.  This  method  appears  to  be  decidedly  promising  (fig.  12). 
By  means  of  this  system  the  water  is  applied  uniformly,  furrowing 
out  is  not  required,  and  once  the  water  is  turned  on  but  little  attention 
is  needed.  A  modified  sprinkler  system  has  been  tried  under  the 
trees,  but  is  not  so  successful  because  the  limbs  usually  have  to  be 
cut  high  to  allow  the  spray  to  spread.  This  leaves  the  trunks  less 
protected  during  coid  weather  and  serious  damage  from  freezing  has 
resulted.  The  cost  of  installing  the  overhead  system  varies  from  $80 
to  $300  an  acre,  according  to  the  type  of  equipment  used. 

The  drip  system  has  been  used  by  some  growers,  but  does  not  give 
an  even  distribution  of  moisture  and  cannot  be  depended  upon  to 
meet  the  requirements  of  the  tree  during  the  growing  season. 


Bulletin  365] 


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599 


As  already  mentioned,  the  question  of  drainage  is  of  equal  im- 
portance with  irrigation.  The  avocado  tree  requires  an  abundance  of 
water,  but  it  must  also  have  thorough  drainage — both  surface  and 
subsoil.     The  tree  is  intolerant  to  standing  water. 


Fig.  12. — The  use  of  overhead  systems  of  irrigation  is  increasing.     The  above 
illustrates  one  of  several  types. 


FEETILIZATION 

Very  little  is  known  concerning  the  fertilization  requirements  of 
the  avocado.  The  conditions  under  which  the  fruit  is  grown  in  Cali- 
fornia are  quite  different  from  those  in  Florida,  consequently  Florida 
experience  is  of  little  value  to  growers  in  this  state.  The  results 
from  the  study  of  fertilizer  requirements  of  citrus  trees  afford  the 
best  information  applicable  at  the  present  time.  A  study  of  the  soils 
in  the  citrus  districts  of  southern  California  has  disclosed  that  they 
are  for  the  most  part  relatively  well  supplied  with  potassium  and 
phosphorus,  two  of  the  three  elements  most  likely  to  be  deficient. 
These  two  require  only  the  presence  of  decaying  organic  matter  to 
make  them  available.  The  soils  are,  however,  prevailingly  deficient 
in  nitrogen  and  organic  matter  and  these  materials  are  applied  to 


600  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

mature  citrus  orchards  in  large  quantities  as  a  demonstrated  means 
of  maintaining  production.  The  same  condition  is  believed  in  general 
to  hold  true  for  the  avocado. 

The  amounts  of  plant  food  elements  removed  from  the  soil  by 
avocado  trees  are  probably  as  large  as  those  removed  by  citrus  trees. 
The  avocado  fruit  is  high  in  mineral  content  and  in  protein,  and  it 
is  not  improbable  that  avocados  remove  more  elements  from  the  soil 
than  a  corresponding  crop  of  citrus  fruits.  The  entire  question  must 
be  given  thorough  scientific  investigation  before  any  definite  state- 
ments can  be  made.  For  mature  bearing  trees,  the  use  of  two  pounds 
of  nitrogen  per  tree  per  year  is  a  safe  minimum;  at  least  half  of 
it  should  be  secured  from  organic  sources,  preferably  bulky  manures. 
No  better  general  fertilizer  can  be  recommended  than  good  barnyard 
manure.  Alfalfa  hay  and  beanstraw  are  likewise  very  satisfactory 
materials  when  they  can  be  secured  at  a  reasonable  price.  These  bulky 
materials  are  best  turned  under  during  the  fall  of  the  year.  With 
citrus  trees  the  use  of  a  quickly  available  nitrogenous  fertilizer,  such 
as  nitrate  of  lime,  has  proved  of  value  in  helping  to  set  the  crop 
when  applied  from  four  to  six  weeks  in  advance  of  the  blossoming 
period.  There  is  some  reason  to  believe  that  a  similar  practice  might 
give  beneficial  results  if  applied  to  the  avocado. 

The  fertilization  of  young  avocado  trees  offers  a  different  problem 
from  that  of  older  trees.  Undoubtedly  the  excessive  use  of  nitrogenous 
fertilizers  has  caused  many  to  delay  coming  into  bearing.  The 
incorporation  of  quantities  of  barnyard  manure  in  the  pits  in  which 
young  trees  are  to  be  planted  is  not  to  be  recommended  except  to  a 
limited  degree  in  very  heavy,  tight  soils.  In  these  cases  the  manure 
should  be  placed  at  the  very  bottom  of  the  pit  and  mixed  thoroughly 
with  the  soil.  Young  trees  will  make  .a  better  growth  if  top  soil  is 
used  to  fill  in  the  holes  and  if  the  use  of  fertilizers  is  withheld  until 
the  trees  have  come  into  bearing.  Exceptions  are  to  be  made,  of 
course,  in  the  case  of  very  poor  soils. 

Cover  crops  have  long  been  used  successfully  as  a  means  of  par- 
tially supplying  the  organic  matter  requirements  of  citrus  trees,  and 
are  being  used  to  some  extent  in  avocado  orchards.  Winter  cover 
cr0ps — usually  purple  vetch  (Vicia  atropurpurea)  or  bitter  clover 
(Melilotus  indica)  are  generally  used  because  of  winter  rainfall. 
Where  irrigation  water  is  plentiful  and  cheap  during  the  summer 
months,  sweet  clover  (Melilotus  alba)  may  be  grown  to  advantage. 
It  is  of  particular  value  on  heavy,  tight  soils,  because  of  the  action  of 
its  large,  deep-growing  roots  in  opening  up  the  subsoil  and  supplying 
organic  matter  and  better  moisture  penetration  to  the  lower  layers. 


BULLETIN  365]  AVOCADO  CULTURE  IN  CALIFORNIA  601 

PRUNING 

No  systematic  study  has  been  made  concerning  the  pruning  of  the 
avocado.  However,  observations  which  have  been  made  over  a  period 
of  some  years  relative  to  different  practices  used  by  growers,  together 
with  principles  applicable  to  other  evergreen  fruit  trees,  point  to 
some  fairly  clear  generalizations.  The  avocado  requires  little  or  no 
pruning  once  its  framework  has  been  established.  Some  thinning  from 
time  to  time  will  be  advisable  to  permit  sunlight  to  reach  the  inside 
foliage.  In  some  strong  growing  varieties  cross  branches  develop 
which,  if  allowed  to  remain,  result  in  poorly  formed  tops  and  severe 
breakage.  Stubbing  back  should  be  avoided,  as  the  resulting  crop  of 
vigorous  sprouts  only  complicates  the  problem.  Mechanically  weak 
growth  should  also  be  removed  early,  in  order  to  eliminate  causes 
of  breakage. 

Little  or  no  heading  back  should  be  given  young  trees.  In  cases 
where  a  head  is  not  naturally  formed  low  enough,  cutting  back  may 
be  necessary.  Examination  of  the  trunk  of  a  young  tree  will  reveal 
several  cycles  of  growth,  each  terminated  by  a  series  of  dormant  buds. 
The  cut  should  be  made  just  above  the  strongest  of  these  buds,  which 
on  starting  usually  make  an  upright  growth.  The  practice  of  head- 
ing back  to  laterals  with  the  hope  of  developing  one  of  these  into  a 
head  has  not  been  successful.  In  some  of  the  weaker  growing  types, 
shortening  in  to  strong  buds  has  been  reported  successful  in  strength- 
ening the  stock  and  framework  of  the  trees  while  young.  Heavy  prun- 
ing of  young  trees  greatly  accentuates  vegetative  growth  and  delays 
the  fruiting  period.  Observations  by  Bioletti  indicate  that  better  tree 
growth  is  obtained  in  young  evergreen  fruit  trees  where  little  or  no 
pruning  is  given,  as  compared  with  trees  more  heavily  pruned. 

HARVESTING 
With  the  varieties  now  grown  in  California,  fruits  are  ripening 
during  every  month  of  the  year.  Since  the  avocado  must  be  ripened 
off  the  tree,  considerable  judgment  is  necessary  in  picking.  With 
the  dark  colored  varieties  little  difficulty  is  experienced  in  telling  when 
the  fruit  is  in  proper  condition,  for  by  the  time  the  skin  is  fairly  well 
colored  it  may  be  safely  picked.  It  is  more  difficult  to  tell  the  best 
time  to  harvest  the  green  varieties,  though  they  lose  the  brightness  of 
color  and  assume  a  dull,  often  slightly  yellowish  caste — the  latter 
cannot  be  relied  upon  entirely.  While  each  variety  has  its  general 
ripening  season,  this  is  not  necessarily  the  same  year  after  year.  Varia- 
tions of  as  much  as  several  weeks  are  not  unusual.     For  the  same 


602  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

variety  the  season  near  the  coast  differs  somewhat  from  the  season 
in  the  interior,  hence  a  careful  inspection  of  the  fruit  itself  is  neces- 
sary to  determine  the  proper  time  for  picking. 

The  regulation  orange  clippers  are  best  suited  for  picking  avocados, 
the  cut  being  made  in  the  swelling  on  the  stem  just  above  the  fruit. 
The  fruit  should  never  be  pulled  from  the  stems  nor  should  it  be 
knocked  off  the  tree.  Ladders  should  be  used  to  pick  the  fruit  out  of 
reach  from  the  ground.  Care  is  necessary  in  handling  to  prevent 
bruising. 

FEOST  INJURY  AND  FROST  PROTECTION 

Owing  to  the  newness  of  the  industry,  comparatively  little  is 
known  relative  to  the  treatment  of  frost  injured  trees.  Varieties 
differ  widely  in  the  degree  to  which  they  withstand  low  temperatures. 
Following  the  severe  cold  weather  of  January,  1922,  observations  were 
made  on  the  various  degrees  of  injury.  Many  trees  that  lost  all  foliage 
but  which  did  not  suffer  injury  to  the  framework  parts  recovered  in 
a  remarkably  short  time.  New  leaves  were  put  out  and  in  some  cases 
bloom,  followed  with  a  small  set  of  fruit  the  same  season.  The  spray- 
ing of  defoliated  trees  with  whitewash  immediately  following  the 
freeze  is  thought  to  have  prevented  sunburn  and  aided  in  recovery. 
Pruning  should  be  delayed  until  all  dying  back  has  ceased ;  cuts  can 
then  be  made  with  certainty.  The  resulting  vigorous  shoots  should  be 
thinned  somewhat,  in  order  to  direct  growth  into  a  smaller  number 
of  well-spaced,  strong  growing  limbs. 

Because  of  the  softness  of  the  heartwood  and  the  readiness  with 
which  it  decays,  large  frost  cracks  and  injured  areas  should  be  care- 
fully cleaned,  disinfected  with  mercuric  chlorid  (corrosive  sublimate) 
solution  of  a  strength  of  1 :1000,  and  painted  over  with  a  waterproof 
covering  such  as  asphaltum  roofing  paint  or  a  rather  soft  grafting 
wax.  Special  attention  should  be  given  such  wounds  as  decay  sets  in 
readily  and  spreads  rapidly.  Where  large  areas  of  bark  and  wood 
are  killed,  it  is  a  question  whether  or  not  the  resulting  mechanical 
weakness  can  ever  be  overcome  sufficiently  to  make  a  satisfactory  tree. 

Frost  injury  may  be  classified  under  three  divisions;  injury  to  the 
blossoms,  injury  to  the  fruit,  and  injury  to  the  tree  itself.  The 
Mexican  varieties  bloom  during  the  winter  and  are  thus  especially 
subject  to  frost  injury  with  the  resulting  loss  of  the  crop,  even  though 
the  trees  themselves  may  not  suffer.  The  Guatemalan  varieties,  on 
account  of  their  later  blooming  period  are  much  less  subject  to  loss  of 
crop  from  frost  injury.  Because  of  its  high  oil  content  the  avocado 
fruit  does  not  readily  freeze.  Heavy  losses  have  occurred,  however, 
due  to  the  freezing  of  the  stems  which  causes  the  fruit  to  drop. 


Bulletin  365]  AVOCADO  CULTURE  IN  CALIFORNIA  603 

The  development  of  varieties  which  bloom  after  the  frost  and 
mature  their  crops  in  eight  to  ten  months  will  materially  reduce  losses. 
Several  such  new  varieties  are  now  under  observation. 

Frost  injury  to  the  tree  itself  may  vary  anywhere  from  the  killing 
of  the  young,  tender  growth  to  the  killing  of  the  tree  down  to  the 
ground.  Aside  from  variety,  the  degree  of  injury  depends  largely 
upon  the  physical  condition  of  the  tree.  In  general  trees  maintained 
under  optimum  growing  conditions  enter  the  winter  in  the  best  con- 
dition to  withstand  cold.  The  maintenance  of  uniform  soil  moisture 
conditions  is  especially  conducive  to  frost  resistance.  Trees  weakened 
from  insufficient  moisture  are  invariably  less  resistant  and  suffer 
more.  The  practice  of  withholding  water  during  the  fall,  supposedly 
to  harden  off  the  trees,  cannot  be  recommended  as  a  sound  practice. 
Trees  thus  handled  are  ready  to  start  into  growth  again  at  the  first 
rain  which  may  occur  in  the  early  winter,  and  are  in  susceptible  con- 
dition for  frost  injury.  The  best  recommendation  that  can  be  made 
is  to  maintain  optimum  soil  moisture  conditions  throughout  the  grow- 
ing season  and  until  the  beginning  of  the  rainy  season. 

There  is  a  pronounced  difference  in  frost  resistance  among  the 
three  races  of  avocados.  The  West  Indian  race  is  much  too  tender 
for  planting  in  California  with  the  exception  of  a  few  favored  locali- 
ties, and  even  there  has  never  produced  satisfactory  fruits.  Studies 
on  the  relative  freezing  points  of  the  cell  sap  of  the  different  races 
show  that  the  sap  of  this  race  freezes  at  higher  temperatures  than  do 
those  of  the  Guatemalan  and  Mexican  varieties.  Of  these,  the  Guate- 
malan is  the  more  tender.3  Prior  to  the  freeze  of  1922  it  was  gen- 
erally believed  that  the  Guatemalan  race  was  as  hardy  as  the.  lemon, 
and  the  Mexican  as  frost  resistant  as  the  orange.  It  is  evident  from 
many  observations  made  following  this  freeze,  that  the  Guatemalan 
varieties  must  be  considered  for  the  most  part  somewhat  more  tender 
than  the  lemon.  Mexican  varieties,  on  the  other  hand,  were  observed 
in  some  localities  to  be  less  injured  than  neighboring  orange  trees, 
while  in  other  localities  somewhat  more  injured.  Two  varieties  espe- 
cially, proved  to  be  outstanding  resistant  and  suffered  little,  injury 
where  they,  had  been  grown,  under  good  cultural  conditions.  .  These 
were  the  Puebla,  a,  thin  skinned.  Mexican  fruit;  and.  the  Fuerte,  a 
Guatemalan  variety  having  a  leathery  skin  and  which  is  apparently 
a  hybrid  with  a  variety  of  Mexican  origin. 


3  Freezing  Point  Lowering  of  the  Leaf  Sap  of  the  Horticultural  Types  of 
Persea  americana.  J.  Arthur  Harris  and  Wilson  Popenoe.  Journal  of  Agri- 
cultural Research,  Vol.  VII,  No.  6,  pp.  261-268,  Nov.  6,  1916. 


604  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

The  behavior  of  these  and  of  varieties  of  the  Mexican  race  in 
general  throughout  the  entire  state  lends  weight  to  the  belief  that 
varieties  of  this  race  will  play  an  important  part  in  the  development 
of  the  commercial  varieties.  It  is  certain  that  they  merit  much  more 
attention  than  has  been  accorded  them  in  the  past. 

Seedlings  of  some  of  the  Guatemalan  trees  now  fruiting  in  south- 
ern California  have  shown  a  hardiness  equal  to  that  of  the  Fuerte, 
and  may  be  of  a  similar  hybrid  origin.  Several  of  these  came  through 
the  freeze  of  1922  unscathed  and  have  commenced  blooming  at  an 
early  age.  One,  at  least,  has  already  produced  superior  fruit.  These 
trees  may  furnish  some  new  varieties  better  suited  climatically  to 
southern  California, 

In  an  industry  that  promises  such  favorable  returns,  frost  pro- 
tection is  deserving  of  more  attention  than  it  has  received.  With 
the  exception  of  higher  hillside  plantings  most  of  the  avocado  orchards 
are  subject  to  periodic  freezing  temperatures.  The  loss  of  the  fruit 
is  of  less  consequence  than  the  injury  to  the  trees.  Adequate  frost 
protection  must  be  considered  a  necessary  feature  of  orchard  manage- 
ment. In  a  very  limited  way  various  methods  of  protection  have 
been  used  including  planting  under  lath,  growing  under  tobacco 
cloth,  and  orchard  heating.  Of  these,  the  latter  alone  has  proved 
satisfactory.  Heaters  of  large  fuel  capacity,  sufficient  to  withstand 
several  days  of  cold  weather,  will  be  necessary.  A  heater  to  each 
tree  will  doubtless  prove  advisable. 

WIND   DAMAGE 

The  avocado  is  subject  to  wind  injury  which  is  manifest  in  break- 
age of  limbs,  in  blowing  off  of  fruit,  and — especially  when  hot,  dry 
winds  occur — in  the  burning  up  of  young  growth  and  the  drying 
out  of  foliage.  The  fruit  may  be  scarred  even  though  not  caused  to 
fall;  this  materially  reduces  its  saleability,  though  not  always  the 
quality. 

Damage  from  wind  prevalence  may  be  reduced  by  the  use  of  lath 
screens,  which  are,  however,  expensive.  Windbreaks  are  a  material 
aid  in  prevention  of  wind  injury,  but  their  use  on  small  plantings  cuts 
down  the  amount  of  available  space  for  trees,  and  increases  the 
amounts  of  water  and  fertilizer  that  must  be  applied  to  maintain  the 
orchard.  The  injurious  effects  to  the  tree  caused  by  excessive  evap- 
oration may  be  minimized  by  the  maintenance  of  good  moisture 
conditions  in  the  soil  at  all  times  and  the  application  of  additional 
water  during  windy  periods. 


Bulletin  365]  AVOCADO  CULTURE  IN  CALIFORNIA  605 


INSECT   PESTS   AND   DISEASES 

The  avocado  in  California  has  been  particularly  free  from  serious 
insect  pests  and  diseases.  Thus  far  spraying  has  not  been  necessary 
for  either  class  of  troubles.  The  common  black  scale  (Saissetia  oleae) 
is  found  quite  commonly  on  the  avocado  but  seldom  in  sufficient 
numbers  to  require  attention.  Condit4  reports  the  occurrence  of  the 
olive  twig  borer  (Polycaon  confertus)  on  a  tree  at  Saratoga,  Santa 
Clara  county.  One  case  of  attack  by  this  insect  has  also  been  reported 
by  Brock  in  Ventura  county,  and  at  the  same  time  a  June  beetle 
(Serica  alternata)  was  reported  injuring  avocado  foliage.  Thrips 
(Heliothrips  haemorrhoidalis)  was  also  found  by  Condit  and  Beers 
in  1917  and  in  1918  badly  infesting  trees  at  Carpenteria,  Santa 
Barbara  county.  Probably  the  jest  most  likely  to  become  serious  is 
the  common  citrus  mealy  bug  (Pseudococcus  citri).  Individual  cases 
of  serious  attack  have  been  reported  in  Los  Angeles  and  Ventura 
counties.  Satisfactory  control  of  this  pest  necessitates  control  of  the 
Argentine  ant  for  which  the  use  of  the  government  formula  arsenic 
syrup  is  recommended.  Severe  infestations  may  require  one  spraying 
or  more  in  addition.5  Unidentified  leaf  miners  have  also  been  noted, 
especially  in  nurseries,  but  their  damage  is  negligible.  Infested 
leaves  and  twigs  should  be  removed  and  burned. 

One  fungous  disease  of  the  avocado  has  been  reported6  caused  by 
a  species  of  Pythiacystis,  similar  to  P.  citrophthera.  It  causes  a  dying 
of  the  bark,  indicated  by  black  areas  from  which  small  beads  of  gum 
appear  and  where  a  white  powdery  substance  is  deposited  on  the 
surface.  Conditions  favorable  for  its  development  are  excessive 
moisture  and  poor  drainage,  most  commonly  found  in  lath  houses. 
The  disease  is  not  at  all  serious  though  occasionally  large  trees  may 
be  attacked.  Dissecting  out  all  affected  tissue  and  disinfecting  with 
Bordeaux  paste  has  proved  a  successful  control  measure. 

Certain  varieties  are  subject  to  severe  cracking  and  discoloration. 
Various  fungi  have  been  isolated  from  such  fruits,  apparently  gaining 
entrance  through  the  broken  skin.  They  have  so  far  not  been  observed 
attacking  sound  fruit. 

4  Insect  Pests  of  the  Avocado.  I.  J.  Condit.  Monthly  Bull.  State  Com.  Hort., 
Vol.  8,  No.  1,  pp.  27-29,  Jan.,  1919. 

s  See  Farmers'  Bulletin  1309,  Control  of  the  Common  Mealybug  of  Citrus  in 
California,  U.  S.  Dept.  Agr.,  Feb.,  1923. 

s  A  Bark  Disease  of  Avocado  Trees.  H.  S.  Fawcett.  Ann.  Kept.  Calif. 
Avocado  Assn.,  p.  152,  1916. 


606  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

SOME  FACTORS  AFFECTING  THE  SETTING  OF  SATISFACTORY  CROPS 
Under  apparently  favorable  environmental  and  cultural  condi- 
tions, it  is  not  uncommon  for  trees  to  fail  to  bear  satisfactory  crops. 
Even  though  bloom  may  be  produced  in  abundance,  fruit  may  fail  to 
set  or  in  the  event  of  setting  may  drop  before  developing  very  far. 
Budded  trees  have  been  known  to  fail  to  bloom  even  though  well 
past  the  usual  bearing  age.  The  causes  accounting  for  these  unsatis- 
factory conditions  are  not  well  understood.  There  have  been  no  long 
continued  investigations  with  the  avocado  looking  toward  their 
solution;   such  investigations   are  greatly  needed. 

Pollination. — One  of  the  factors  that  undoubtedly  has  much  to 
do  with  the  problem  is  that  of  pollination.  Its  importance  in  other 
fruit  industries  is  well  understood..  Preliminary  work  in  Florida7 
indicates  that  cross  pollination  may  be  necessary  with  some  varieties 
in  that  state.  Investigations  being  conducted  in  southern  California 
at  the  present  time  by  Dr.  A.  B.  Stout  of  the  New  York  Botanic 
Gardens  have  already  given  some  very  valuable  information  on  the 
habits  of   avocado  flowers.     Present  evidence   indicates  that : 

1.  Avocado  flowers  tend  to  open  in  unison  and  to  open  for  two  distinct 
periods  at  different  times  during  the  twenty-four  hours. 

2.  The  pistil  is  more  apt  to  be  receptive  during  the  first  period  than  the 
second,  during  which  latter  period  the  pollen  is  usually  shed. 

3.  In  a  number  of  varieties  there  is  a  marked  tendency  for  few  if  any 
flowers  to  be  open  for  the  first  time,  when  flowers  open  for  the  second  time  are 
shedding  pollen.  .... 

4.  Varieties  differ  greatly  in  the  length  of  time  during  which  flowers  are 
open,  and  in  the  time  of  day  when  flowers  open,  both  for  the  first  and  for 
the  second  time. 

5.  In  a  few  varieties  a  considerable  over-lapping  between  the  two  periods 
of  opening  occurs,  making  possible  self-pollination. 

6.  Apparently,  self-sterility,  or  incompatability  exists  with  a  number  of 
varieties,  even  if  pollen  is  applied  when  the  pistil  is  receptive;  this,  renders 
cross-pollination  necessary. 

7.  The  state  of  the  weather  has  a  decided  effect  upon  the  time  of  opening, 
upon  the  period  over  which  flowers  remain  open,  and  upon  the  time. and  manner 
of  the  shedding  of  pollen.  •     ,  •  •■ 


From  these  observations  it  can  be  seen  that  fruit  settilig..wi]I. be 
much  more  certain  if  compatible  varieties  are  inter- 'planted,  the 
flowers  of  which  open  at  such  times  as  will  permit  of  cross-pollination. 
The  discovery  of  self -compatible  varieties  with  opening  periods  which 
overlap,  would  greatly  simplify  the  problem.  The  studies  have  not 
progressed  far  enough  to  know  all  the  combinations  of  flower  opening 


7  Investigations  in  Avocado  Breeding.     B.  S.  Nirody.     Annual  Report  Cali- 
fornia Avocado  Association,  1922,  pp.  65-78. 


Bulletin  365]  AVOCADO  CULTURE  IN  CALIFORNIA  607 

and  compatibility.  At  the  present  time  the  Fuerte  and  the  Dickinson 
seem  particularly  well  adapted  to  each  other.  Combinations  more 
nearly  equal  in  frost  resistance,  however,  would  be  better.  Until 
specific  recommendations  can  be  made  with  assurance,  mixed  plant- 
ings of  many  varieties  seem   desirable. 

The  top-working  of  two  or  more  compatible  varieties  into  the 
same  tree  may  prove  one  of  the  most  satisfactory  methods  of  securing 
results.  Varieties  differ  in  the  ease  with  which  they  may  be  top- 
worked  and  in  their  subsequent  growth.  This  condition  will  have 
to  be  taken  into  account  and  congenial  varieties  used,  if  this  means 
of  securing  proper  pollination  is  to  be  successful. 

The  presence  of  many  bees  also  evidently  bears  an  important 
relation  to  pollination  and  it  may  prove  desirable  to  maintain  hives 
within  avocado  orchards. 

The  investigations  now  under  way  give  promise  of  solving  a 
number  of  perplexing  problems  connected  with  the  securing  of  a 
satisfactory  set  of  fruit. 

Bud  Selection. — It  has  long  been  known  that  the  avocado  is  subject 
to  bud  variation.  Black  Ganter  fruits  are  consistently  produced  on 
one  limb  of  a  large  tree  in  Whittier.  Round  forms  of  the  Fuerte 
have  been  discovered  on  standard  trees.  Such  occurrences  indicate 
the  desirability  of  using  care  in  the  selection  of  bud  wood.  In  the 
early  clays  of  the  industry  buds  were  taken  from  any  kind  of  wood 
available  and  from  any  source  convenient,  with  resulting  wide  vari- 
ation in  the  type  and  quality  of  trees  produced.  At  the  present 
time  nurserymen  are  giving  very  careful  attention  to  the  selection 
of  wood  from  thrifty,  good  producing  trees,  and  the  type  of  nursery 
trees  now  being  grown  testifies  to  the  value  of  this  practice.  Some 
work  has  been  started  along  the  lines  of  tree  record  keeping  with 
the  purpose  of  locating  high  producing  parent  trees.  Such  work 
will  be  handicapped  until  there  is  a  sufficient  number  of  trees  growing 
under  identical  orchard  conditions  to  eliminate  environmental  factors 
and  make  detection  of  inherent  variations  certain. 

June  Drop. — Severe  shedding  of  the  young  fruits  has  been  noted 
during  hot  weather  and  is  not  an  uncommon  cause  of  the  low  yields 
sometimes  received.  This  trouble  is  especially  severe  in  the  Navel 
orange.  Investigations  by  Coit  and  Hodgson8  have  shown  that  it 
is  ordinarily  caused  by  the  excessive  evaporation  that  takes  place 
from  the  leaf  surface  during  periods  of  hot  or  dry  atmospheric 
conditions.    The  root  system  is  unable  to  supply  moisture  fast  enough 

s  An  Investigation  of  the  Abnormal  Shedding  of  Young  Fruits  of  the 
Washington  Navel  Oranges.  J.  Eliot  Coit  and  Robert  W.  Hodgson.  Univ.  of 
Calif.  Publ.  in  Agri.  Sci.,  Vol.  3,  No.  11,  pp.  283-368,  April,  1919. 


608  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

under  such  conditions  and  water  is  withdrawn  from  the  young  fruits 
to  make  up  the  deficiency,  with  the  result  that  they  are  weakened  and 
drop  off.  A  spring  cover  crop,  grown  to  furnish  a  good  ground 
covering  by  June,  has  been  found  under  certain  conditions  to  cut 
down  the  temperature  materially  within  the  orchard  and  reduce  the 
drop.  Purple  vetch  planted  early  in  March  has  given  the  best 
growth  of  any  crop  yet  tried  for  this  purpose.  The  extent  to  which 
this  factor  affects  the  avocado  has  not  yet  been  determined,  but  in 
all  probability  it  has  an  important  bearing  on  the  failure  to  secure 
satisfactory  crops. 

Rootstocks. — The  importance  of  desirable  rootstocks  has  already 
been  mentioned.  Sufficient  attention  to  securing  the  most  congenial 
stocks  has  not  been  given  in  the  past.  Certain  varieties  make  very 
poor  unions  with  stocks  at  present  used  and  fail  to  make  satisfactory 
trees.  In  this  connection  it  is  interesting  to  note  a  reaction  observed 
in  the  W.  A.  Spinks  orchard  at  Duarte.  A  number  of  large  Harman 
trees  were  budded  over  to  the  Murrieta  variety,  and  failing  to  make 
satisfactory  growth,  were  topped  and  budded  to  the  Spinks  variety. 
Two  or  three  of  the  Murrieta  buds  were  overlooked  and  when  the 
vigorous  growing  Spinks  buds  began  to  develop  a  thrifty  top,  the 
Murrieta  buds  were  stimulated  into  active  growth,  put  out  strong 
branches,  and  have  since  borne  good  crops. 

Studies  with  citrus  and  deciduous  fruits  have  indicated  the  close 
relation  to  vigor  and  production  that  congeniality  of  stock  and  scion 
maintain.  This  phase  of  development  of  satisfactory  yielding  trees 
awaits  thorough  investigation. 

Girdling. — Girdling  has  been  resorted  to  as  a  means  of  stimulating 
fruit  production  on  otherwise  barren  trees.  Successful  results  have 
been  obtained  in  some  cases  and  in  others  none  whatever.  The  Taft 
variety  which  has  been  conspicuous  for  its  delay  in  coming  into 
bearing  has  been  the  object  of  such  experimentation  more  than  any 
other.  A  number  of  growers  have  succeeded  in  getting  fruit  to  set 
in  abundance  on  girdled  limbs  while  the  rest  of  the  tree  failed  to 
produce.  Girdling  is  best  done  in  October.  A  ring  of  bark  varying 
from  an  eighth  to  a  quarter  of  an  inch  in  width  is  removed  usually 
near  the  base  of  the  limb;  a  ring  of  this  size  will  readily  heal  over. 
Apparently  the  downward  flow  of  sap  is  checked  and  the  storage 
of  food  materials  stimulates  fruit  production.  Girdling  is  still  largely 
in  the  experimental  stage,  however,  and  cannot  be  considered  as  the 
solution  of  the  many-sided  problem  of  rendering  barren  trees  fruitful. 
It  has  the  disadvantages  of  lowering  the  resistance  to  frost  of  the  limb 
girdled,  and  of  weakening  the  roots  through  subjecting  them  to  a 
period  of  partial  starvation. 


BULLETIN  365]  AVOCADO  CULTURE  IN  CALIFORNIA  609 


MAEKETING 

The  first  essential  to  the  successful  marketing  of  any  fruit  in 
commercial  quantities  is  a  standard  product  of  uniformly  good 
quality.  Thus  far  the  supply  of  California  grown  avocados  has  not 
been  great  and  marketing  has  not  required  special  attention.  As 
evidence  of  this  fact,  the  avocado  has  never  received  mention  in  the 
various  fruit  and  vegetable  Standardization  Acts,  setting  forth  the 
grades  under  which  certain  fruits  and  vegetables  must  be  prepared 
for  market.  The  placing  on  the  market  of  immature  fruit  and  wind- 
falls, however,  has  reacted  unfavorably  to  the  industry,  and  should 
be  discontinued.  The  same  result  has  come  from  the  sale  of  over- 
ripe and  inferior  imported  fruits.  Just  what  standards  should  be 
used  in  determining  maturity  is  a  question  not  yet  decided.  The  work 
of  E.  M.  Chace  and  C.  G.  Church,  of  the  United  States  Department 
of  Agriculture,  and  of  M.  E.  Jaffa,  of  the  University  of  California, 
has  laid  a  good  foundation  for  arriving  at  some  definite  conclusions 
regarding  the  ripening  of  most  of  the  commercial  varieties.  The 
season  of  ripening  varies  somewhat  from  year  to  year,  consequently 
no  rigid  monthly  schedule  can  be  drawn.  The  determination  of 
suitable  maturity  standards  and  strict  adherence  to  them  are  basic 
to  the  success  of  the  industry. 

The  subject  of  varieties  will  be  discussed  in  detail  in  another 
section,  but  it  should  be  mentioned  here  that  adherence  to  a  relatively 
small  number  of  standard  varieties  is  of  importance  to  the  develop- 
ment of  satisfactory  markets.  The  work  of  the  Committee  for  the 
Registration  and  Classification  of  Varieties  of  the  California  Avocado 
Association  has  already  resulted  in  considerable  progress  in  this 
direction. 

The  place  of  the  thin-skinned  Mexican  fruit  on  the  commercial 
market  has  been  more  or  less  problematical.  The  fruit  is  finer  in 
flavor,  and  often  in  quality,  than  many  of  the  larger  Guatemalan 
fruits.  It  comes  on  the  market  at  a  good  time  of  the  year  and  can 
be  shipped  very  satisfactorily  if  given  a  little  extra  care.  Objections 
to  the  small  size  of  most  varieties  of  this  group  can  be  overcome  by 
the  introduction  of  large-sized  varieties  known  to  exist  elsewhere 
(fig.  13).  Some  of  these  are  now  under  trial.  For  local  markets 
and  for  home  use  they  have  a  very  definite  place.  No  general  pre- 
diction can  be  made  as  to  their  future  commercially,  until  the  market 
has  been  exploited  and  the  tastes  of  consumers  determined. 

California  grown  avocados  must  meet  the  competition  of  Florida 
and  West  Indian  fruits,  which,  with  the  exception  of  the  Trapp  and 


610  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

a  few  others,  ripen  during  the  summer  months,  when  there  is  an 
abundance  of  other  fruits  of  all  kinds;  accordingly  the  price  is  lower 
than  at  any  other  time  of  the  year.  The  best  market  is  to  be  had 
during  the  winter  months,  and  it  is  this  market  that  is  of  particular 
interest  to  the  California  grower,  as  he  already  has  varieties  that 
mature  at  this  season.  With  the  establishment  of  the  avocado  as  an 
important  article  of  food  rather  than  a  luxury,  an  all-year-round 
demand  will  be  created.  Future  commercial  production  must  take 
this  condition  into  account.  At  the  present  time  there  is  sufficient 
variation  in  season  among  the  varieties  in  California  to  furnish  ripe 
avocados  for  every  month  of  the  year. 

No  standard  packing  crate  has  been  developed  for  the  handling 
of  California  avocados,  since  most  of  the  fruit  is  absorbed  by  the 
local  markets.  The  thirty -pound  lug  box,  padded  with  excelsior  and 
packed  with  two  layers  of  fruit  is  most  commonly  used.  In  Florida 
the  standard  tomato  crate,  12  x  12  x  24  inches,  is  ordinarily  used, 
carrying  two  to  four  dozen  fruits,  according  to  size.  An  excelsior  pad 
is  used  on  the  bottom  and  top.  No  paper  wrapping  is  used  since 
this  has  been  found  to  hold  heat  and  hasten  ripening  while  in  transit. 
Fruits  so  packed  are  shipped  across  the  continent  without  any  loss 
or  trouble. 

Experiments  indicate  that  the  avocado  will  keep  at  temperatures 
of  32  to  35  degrees  F.  for  periods  as  long  as  two  months.  With  an 
increasing  supply  of  fruit  the  problem  of  storage  will  doubtless 
become  more  important. 

At  the  present  time  a  marketing  arrangement  has  been  effected 
by  the  California  Avocado  Association  whereby  the  fruit  of  most  of 
its  members  is  marketed  through  one  of  the  large  marketing  agencies 
having  branches  throughout  the  United  States.  It  is  handled  on  a 
strictly  commission  basis,  the  members  reserving  the  right  to  market 
such  fruit  as  they  desire  locally  and  to  the  hotel  trade.  No  great 
amount  of  fruit  has  been  available  at  any  one  time,  so  that  the 
marketing  problem  has  not  been  difficult.  With  the  prospects  of 
fairly  large  crops  of  spring  and  summer  fruit,  coming  into  competi- 
tion with  all  other  kinds  of  fruit  as  well  as  avocados  from  Florida 
and  the  West  Indies,  one  of  the  immediate  problems  confronting  the 
industry  is  that  of  creating  a  greater  consumer  demand.  The  experi- 
ence of  the  other  organized  fruit  industries  in  meeting  similar 
situations  will  be  of  great  help  in  popularizing  the  avocado. 


Bulletin  365] 


AVOCADO  CULTURE  IN  CALIFORNIA 


611 


Fig.  13. — Tamayo  Avocado  (S.  P.M.  54270).  A  large  fruited,  thin-skinned 
variety  discovered  by  Wilson  Popenoe  in  the  Chota  Valley,  Ecuador.  The.  fruits 
weigh  as  high  as  18  ounces. 

The  discovery  of  these  large  fruited  varieties  in  Ecuador  is  of  particular 
promise  for  the  expansion  of  the  area  in  California  in  which  the  avocado  may 
become  commercially  profitable.     (Photo  by  Popenoe.) 


612  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

EACES  AND  VAKIETIES 
Races. — As  previously  indicated  there  are  three  general  groups 
of  avocados  growing  in  the  United  States,  for  convenience  loosely 
termed  the  West  Indian,  Guatemalan,  and  Mexican  races,  though  not 
strictly  separate  horticultural  races  in  the  technical  sense  of  the 
term.  Of  these  three  races,  two  only  are  of  commercial  importance 
in  California — the  Mexican  and  the  Guatemalan.  Popenoe9  has 
classified  these  groups  as  follows: 

1.  Leaves  anise-scented;  skin  of  fruit  thin  (rarely  more  than  yi2  inch  in  thick- 
ness).    Persea   drymifolia. 

MEXICAN  RACE  OF  HORTICULTUKE 

2.  Leaves  not  anise-scented;  skin  of  fruit  thicker  (from  y32  to  y±  inch  in 
thickness).  Persea  americana. 

(a)  Fruit  summer  and  fall  ripening;  skin  usually  not  more  than  y1G  inch 
thick,  lea'thery  in  texture. 

WEST  INDIAN  RACE 

(6)  Fruit  winter  and  spring  ripening;  skin  y1Q  to  *4  inch  thick,  woody  in 
texture. 

GUATEMALAN  RACE 

At  least  one  variety  intermediate  in  form  between  the  Guatemalan 
and  Mexican  races  has  appeared — the  Fuerte,  an  apparent  hybrid 
between  these  two  groups.  Other  intermediate  forms  found  in 
Central  America  and  Mexico  are  at  the  present  time  unclassified. 

The  West  Indian  race  is  unsuited  climatically  to  California  con- 
ditions, as  evidenced  by  the  failure  of  the  plantings  tried  in  the  past, 
and  may  be  disregarded  as  far  as  its  economic  importance  in  this 
state  is  concerned.  Belonging  as  they  do  to  two  different  species, 
the  important,  outwardly-evident,  botanical  differences  serve  to  dif- 
ferentiate the  Guatemalan  and  Mexican  races  horticulturally.  The 
leaves  of  the  Mexican  race  are  usually  smaller  than  those  of  the 
Guatemalan,  and  are  sharper  at  the  apex.  They  have  the  character- 
istic anise  odor  when  crushed  which  is  entirely  lacking  in  the  Guate- 
malan race.  This  property  is  also  characteristic  of  the  immature 
Mexican  fruits.  The  fruits  of  the  Mexican  race  are  smaller,  rarely 
reaching  a  pound  in  weight,  are  smooth,  dark  green  to  purple  in 
color,  and  often  glossy.  They  mature  usually  from  August  to 
December  from  nine  to  ten  months  after  blooming.  The  seed  is 
commonly  larger  in. proportion  to  the  edible  part  of  the  fruit  than 
that  of  the  Guatemalan.    The  two  seed  coats  are  thin,  sometimes  closely 

s  Manual  of  Tropical  and  Sub-Tropical  Fruits.  Wilson  Popenoe.  P.  66,  1920. 
The  Macmillan  Co.,  New  York. 


Bulletin  365] 


AVOCADO  CULTURE  IN  CALIFORNIA 


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614  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

united  and  adhering1  to  the  cotyledons,  and  sometimes  separating. 
The  flowers  appear  during  the  winter  and  early  spring,  and  are 
subject  to  frost  injury  in  severe  winters.  Occasionally  late  flowers 
appear  and  furnish  a  light  second  crop  in  the  early  spring. 

The  fruit  of  the  Guatemalan  race  is  large,  averaging  from  12  to  20 
ounces,  some  varieties  attaining  a  weight  of  more  than  three  pounds. 
It  varies  in  color  from  green  to  purplish  or  reddish  black.  The 
surface  while  sometimes  fairly  smooth,  is  usually  rough  and  somewhat 
warty  and  coarsely  granular  in  texture.  The  seed  fits  tightly  into  the 
cavitjr,  its  seed  coats  are  thin,  united,  and  adherent  to  the  cotyledons 
throughout.  The  flowers  appear  later  than  those  of  the  Mexican 
race,  usually  after  most  danger  from  frost  is  past.  The  fruit  matures 
from  twelve  to  eighteen  months  after  the  blossoming  season. 

Varieties. — Many  varieties  of  both  the  Guatemalan  and  the 
Mexican  groups  are  fruiting  in  California  at  the  present  time — the 
number  is  well  over  one  hundred.  Because  of  their  greater  resistance 
to  cold,  the  Mexican  varieties  enjoy  a  much  wider  range  of  planting. 
In  choosing  varieties  for  commercial  planting  certain  general  char- 
acteristics are  to  be  desired  in  both  the  tree  and  the  fruit.  The  tree 
itself  must  be  adapted  to  the  location  selected.  It  should  be  a  hardy 
and  vigorous  grower,  forming  a  well  balanced  head  capable  of  carry- 
ing good  sized  crops  without  breakage.  It  should  be  readily  pro- 
pagated and  easily  handled  in  the  nursery.  It  should  produce 
sufficiently  good  crops  consistently,  to  be  commercially  profitable, 
and  should  come  into  bearing  at  a  reasonably  early  date.  Varieties 
that  have  come  into  bearing  at  too  early  a  period,  however,  have  a 
tendency  to  expend  their  energies  in  flowering  and  premature  pro- 
duction at  the  expense  of  tree  development.  The  first  few  years 
of  the  life  of  any  fruit  tree  should  be  primarily  devoted  to  the 
building  up  of  a  strong  tree  capable  of  sustained  production  over 
a  long  period  of  years,  rather  than  to  the  early  production  of  fruit. 

The  length  of  time  between  blooming  period  and  maturity  is  also 
an  important  consideration.  Most  of  the  thin-skinned  fruits  mature 
from  nine  to  twelve  months  after  blooming;  on  the  other  hand  few 
of  the  Guatemalans  mature  under  fourteen  months,  several  requiring 
eighteen.  Two  of  the  new  Guatemalan  varieties — the  Ward  and  the 
Dorothea — bloom  in  the  spring  and  mature  their  fruit  in  the  fall 
and  winter  of  the  same  year.  In  developing  new  varieties  this 
question  is  one  that  should  receive  consideration. 

Many  varieties  now  fruiting  in  southern  California  have  been 
noted  to  have  a  more  or  less  pronounced  habit  of  alternate  bearing. 
Popenoe  reports  this  condition  quite  general  among  the  avocados  in 


Bulletin  365] 


AVOCADO  CULTURE  IN   CALIFORNIA 


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616  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

Guatemala.  Thinning"  of  fruit  during  the  heavy  producing  years 
may  aid  in  maintaining  a  more  uniform  annual  production.  No 
experiments  have  been  conducted  with  the  fruit  along  this  line. 

The  market  demands  are  important  in  considering  the  fruit  itself. 
A  medium-sized  fruit,  attractive  in  color,  uniform  in  shape  and  readily 
packed,  of  good  quality  and  pleasing  flavor,  fits  the  market  require- 
ments at  the  present  time.  The  seed  should  not  be  large  and  should 
preferably  be  tight  in  the  cavity.  To  meet  the  highest  prices  the 
fruit  should  mature  during  the  winter  and  early  spring  months;  at 
this  season  of  the  year  less  competition  is  met  with  other  kinds  of 
fruits  and  with  avocados  imported  from  the  West  Indies. 

The  matter  of  selecting  varieties  is  one  of  considerable  perplexity. 
The  industry  has  been  fortunate  in  its  early  history,  in  having  an 
active  growers'  organization,  the  California  Avocado  Association, 
working  in  its  interests.  The  Association  early  organized  a  Committee 
for  the  Registration  and  Classification  of  Varieties,  whose  duty  it 
has  been  to  study  the  behavior  of  the  different  varieties  over  a  period 
of  years  and  to  make  recommendations  according  to  its  observations. 
The  list  of  recommended  varieties  prepared  by  this  committee  offers 
the  safest  guide  to  commercial  planting  at  the  present  time.  That 
it  will  change  from  time  to  time  goes  without  saying;  changes  have 
already  been  made.  The  varieties  that  will  be  planted  in  the  future 
will  in  all  probability  be  quite  different  from  most  of  those  planted 
now.  Recommendations  can  be  made  only  for  the  present.  In  the 
past  as  new  seedlings  have  come  into  bearing,  enthusiastic  owners 
have  quite  naturally  become  interested  in  their  commercial  possibil- 
ities. Many  varieties  have  been  propagated  and  trees  sold  prematurely. 
The  result  is  that  there  are  many  named  varieties  today  which  have 
already  been  discarded,  and  probably  many  of  those  now  grown 
will  hardly  be  known  ten  years  from  now. 

The  descriptions  of  the  varieties  on  the  present  recommended  list 
of  the  Variety  Committee  of  the  Avocado  Association  are  given  below. 
This  list  is  no  way  to  be  considered  a  permanent  one;  indications 
are  that  some  changes  will  probably  be  made  in  the  near  future. 
It  represents  what  are  considered  the  best  proven  varieties  at  the 
present  writing.  The  ripening  period  indicated  for  each  is  subject 
to  considerable  variation  from  year  to  year  depending  upon  seasonal 
variations  in  weather  conditions. 

Fuerte  (fig.  14). — Form  pyriform  (not  necked)  to  oblong;  size 
below  medium  to  above  medium,  weight  10  to  16  ounces,  length  4  to 
41/2  inches,  greatest  breadth  2*/2  to  2%  inches ;  base  pointed ;  the  stem 
inserted  obliquely  in  a  small  shallow  cavity ;  apex  obliquely  flattened, 


Bulletin  365 


AVOCADO  CULTURE   IN   CALIFORNIA 


617 


618  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

depressed  around  the  stigmatic  point ;  surface  pebbled,  sometimes 
slightly  wrinkled  around  the  stem,  dull  green,  with  numerous,  small 
yellow  dots;  skin  about  Vzi  inch  thick,  separating  readily  from  the 
flesh,  pliable  and  leathery  in  texture ;  flesh  rich  cream  yellow  in  color, 
greenish  near  the  skin,  of  smooth  buttery  texture,  and  very  rich 
flavor ;  quality  excellent ;  seed  medium,  tight  in  cavity,  seed  coats 
closely  surrounding  cotyledons.  Season  January  to  May  in  southern 
California,     ( Popenoe ) . 

Originated  at  Atlixco,  state  of  Puebla,  Mexico;  introduced  into 
California  in  1911.  The  tree  is  unusually  vigorous,  hardy  and  pro- 
ductive. Its  season  of  ripening  is  exceptionally  long.  The  fruit 
contains  30%  of  oil,  is  of  fine  flavor  and  quality.  This  variety  and 
the  Puebla  described  below,  were  the  two  outstandingly  hardy  vari- 
eties on  the  recommended  list  of  the  Avocado  Association  that  emerged 
from  the  severe  cold  wave  of  1922  with  comparatively  little  injury. 
The  Fuerte  is  apparently  a  natural  hybrid  between  the  Guatemalan 
and  Mexican  races,  though  final  proof  of  this  assumption  is  yet  to 
be  made.     It  partakes  of  the  characteristics  of  both  races. 

Puebla  (fig.  15). — Form  obovoid,  slightly  oblique;  size  below 
medium  to  medium,  weight  8  to  10  ounces,  length  3y2  inches,  greatest 
breadth  2V8  inches ;  base  obliquely  flattened,  the  stem  inserted  slightly 
to  one  side  in  a  small  shallow  cavity ;  apex  obliquely  flattened  but  not 
prominently  so;  surface  smooth,  glossy,  deep  maroon-purple  in  color, 
with  numerous  reddish  dots ;  skin  less  than  %2  inch  thick,  easily  peeled 
from  the  flesh,  firm  in  texture ;  flesh  rich  cream  yellow  near  the  seed, 
changing  to  pale  green  near  the  skin,  buttery  in  texture,  and  of  rich 
nutty  flavor;  quality  very  good,  seed  medium  to  large,  tight  in  the 
cavity,  with  both  seed-coats  adhering  closely  to  the  cotyledons.  Season 
December  to  February  in  southern  California.     (Popenoe.) 

Originated  at  Atlixco,  state  of  Puebla,  Mexico ;  introduced  and  first 
propagated  in  California  in  1911.  The  tree  is  exceptionally  hardy  and 
vigorous,  and  well  balanced  in  form.  It  fruits  later  in  the  season 
than  most  others  of  the  Mexican  race.  The  Puebla  and  Fuerte  proved 
to  be  the  hardiest  commercial  varieties  yet  discovered  as  shown  by 
the  severe  freeze  in  1922.     Oil  content  26.45%. 

8 pinks  (fig.  16). — Form  broadly  obovate,  or  obconic;  size  large, 
weighing  from  16  to  30  ounces,  length  about  5  inches;  base  narrow, 
rounded  with  the  rather  short,  stout  stem  inserted  almost  squarely 
without  depression;  apex  rounded;  surface  roughened,  warty  around 
the  base,  dark  purple  in  color ;  skin  thick,  separating  readily  from 
the  flesh,  woody,  granular,  brittle;  flesh  firm,  smooth,  rich  yellow  in 
color,  free  from  fibre,  and  of  rich  pleasant  flavor ;  quality  very  good ; 
seed  nearly  spherical,  large,  weighing  3  ounces,  fitting  tisrhtly  in  th» 
cavity  with  the  seed  coats  adhering  closely.  Season  April  to  August 
at  Duarte,  California, 

Originated  at  Duarte,  California,  from  seed  secured  from  Mazat- 
lan,  Mexico ;  first  propagated  in  1915.  The  tree  is  extremely  vigorous 
and  productive  and  of  fine  orchard  form ;  the  fruit  is  of  excellent 
quality.     Oil  content  18y2%. 


Bulletin  365] 


AVOCADO  CULTURE   IN   CALIFORNIA 


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620  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

Dickinson  (fig.  17). — Form  oval  to  obovate,  sometimes  almost  pyri- 
form ;  size  small  to  medium,  weight  9  to  14  ounces,  length  3y2  inches, 
greatest  breadth  2%  inches;  base  not  noticeably  flattened,  the  long 
stem  inserted  in  a  very  small  and  shallow  cavity;  apex  rounded; 
surface  very  rough,  verrucose  or  tuberculate  around  the  base,  dark 
purple  in  color  with  large,  irregular,  maroon  dots;  skin  very  thick, 
especially  near  the  base,  separating  fairly  readily  from  the  flesh, 
coarsely  granular,  woody,  brittle;  flesh  buttery,  pale  greenish  yellow, 
free  from  fiber,  of  pleasant  flavor ;  quality  good ;  seed  roundish  oblate, 
medium  sized,  tight  in  cavity,  with  both  seed-coats  adhering  closely. 
Season  April  to  October  at  Los  Angeles,  California.     (Popenoe.) 

Originated  at  Los  Angeles,  California;  first  propagated  in  1912. 
Vigorous  in  growth,  and  precocious  in  fruiting.  Oil  content  14.4%. 
Near  the  coast  this  fruit  frequently  holds  on  until  December. 

Sharpless  (fig.  18). — Form  slender  pyriform  to  elongated  pyri- 
form  with  a  long  neck ;  size  large  to  very  large,  weight  16  to  24  ounces, 
length  6  to  6%  inches,  greatest  breadth  S1/^  inches;  base  very  narrow, 
the  long  stem  inserted  obliquely  without  depression;  apex  rounded; 
surface  slightly  roughened  or  pitted,  glossy,  greenish  purple  to  deep 
purple  in  color,  with  numerous  yellowish  dots;  skin  thick,  separating 
readily  from  the  flesh,  granular  and  woody ;  flesh  smooth,  firm,  cream 
colored,  free  from  fibre  discoloration,  and  of  unusually  rich  pleasant 
flavor ;  quality  excellent ;  seed  oblate-oblique,  small  to  medium,  weigh- 
ing 2  ounces,  fitting  tightly  in  the  cavity,  with  both  seed-coats  adhering 
closely.  Season  October  to  February  at  Santa  Ana,  California. 
(Popenoe.) 

Originated  near  Santa  Ana,  California;  first  propagated  in  1913. 
This  is  a  fruit  of  fine  quality,  ripening  very  late  in  the  season.  The 
fruit  requires  eighteen  months  from  the  blooming  period  for  maturity. 
Young  trees  require  special  care  in  handling  in  windy  sections  in 
order  to  develop  strong,  vigorous  framework.     Oil  content  18%. 

In  addition  to  the  fruits  on  the  approved  list  the  following  are 
some  of  the  more  promising  seedling  varieties  under  observation  that 
may  become  commercial.  (These  notes  are  from  Report  of  the  Com- 
mittee on  Registration  and  Classification  of  Varieties  of  the  Avocado 
Association.) 

Ward. — Originating  at  Sierra  Madre  at  the  place  of  Irving  N. 
Ward.  Tree  ten  years  old,  and  has  borne  crops  from  its  fourth 
year.  The  tree  propagates  readily ;  young  trees  have  borne  at  three 
years.  Fruit  pyriform,  dark  red  to  purple  in  color,  skin  rather  thin. 
Flesh  cream  yellow  to  green,  quality  good,  flavor  good,  some  samples 
showing  a  trace  of  bitterness.  Season  beginning  in  February.  Tree 
fairly  hardy.  The  variety  matures  its  fruit  in  eight  to  ten  months 
from  the  blossoming  period. 

Dorothea. — This  tree  is  a  seedling  of  the  old  Miller  tree,  and  is 
growing  on  the  A.  W.  Miller  place  in  Hollywood.  It  is  believed  to  be 
a  cross  between  the  Miller  and  one  of  the  small-fruited  Mexican  trees 


Bulletin  365] 


AVOCADO  CULTURE  IN  CALIFORNIA 


621 


622  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

in  the  vicinity.  It  is  vigorous  and  very  productive,  blossoms  in  April 
and  May,  and  ripens  its  fruit  mainly  in  December  and  January.  The 
fruit  weighs  from  8  to  12  ounces.  It  is  light  green  in  color,  with 
many  yellowish  dots.  Skin  leathery;  flesh  clear,  attractive  yellow, 
free  from  fibre;  flavor  excellent,  quality  very  good. 

Button. — Tree  tall,  large,  fairly  hardy.  Fruit  approximately 
a  pound  in  weight ;  form  pyriform,  very  slightly  necked ;  skin  warty, 
Vza  inch  thick;  color  dark  maroon,  with  dots  of  lighter  color.  Flesh 
cream  to  light  green  in  color,  smooth,  with  a  trace  of  fibre,  flavor 
very  rich.     Fruit  matures  during  the  spring.     Oil  content  16%. 

Thompson. — Originating  at  Montebello  from  seed  secured  from 
Atlixco.  Parent  tree  now  11  years  of  age.  Fruit  approximately  a 
pound  in  weight ;  pyrif  orm,  color  reddish  purple  ;  skin  V\i  inch  thick ; 
flesh  light  yellow  to  light  green,  some  red  fibre  showing,  quality  good, 
flavor  watery.     Ripening  season  February  1  to  April  1. 

Prince. — This  tree  is  growing  on  the  place  of  E.  W.  Dickey  in 
Hollywood.  Form  pyriform,  weight  21  ounces,  seed  2y2  ounces,  tight 
in  cavity ;  color  green,  with  brown  dots ;  skin  granular,  Viq  inch  thick ; 
quality  good,  flavor  excellent.     Season  October  to  December. 

Billingsley. — Parent  tree  on  place  of  Ray  Billingsley,  Villa  Park. 
Form  pyriform  to  oval,  weight  10  to  16  ounces;  color  light  yellowish 
green  turning  partially  brown ;  flesh  clear,  bright  yellow,  with  a  trace 
of  fibre,  quality  and  flavor  excellent.    Fruit  ripens  during  the  spring. 

Dickey  A. — Fruit  pyriform,  medium  in  size,  weighing  from  12 
to  16  ounces;  color  red  to  reddish  purple,  skin  thick  and  tough;  flesh 
bright,  clear  yellow,  smooth  in  texture ;  flavor  and  quality  very  good ; 
seed  very  small.  Season  May  to  July.  Originated  at  Hollywood. 
Tree  a  vigorous  grower.  This  fruit  ranks  as  one  of  the  highest  in 
the  smallness  of  its  seed  as  compared  with  the  rest  of  the  fruit. 

Tiger. — This  variety  is  especially  noteworthy  as  it  has  succeeded 
in  withstanding  the  hot,  dry,  interior  climate  better  than  any  other 
to  date.  The  tree  is  a  hardy,  upright  grower.  The  fruit  is  about 
three-quarters  of  a  pound  in  weight,  purple  in  color,  and  pear-shaped. 
The  flavor  is  neutral  but  agreeable.  The  skin  is  thick  and  the  seed 
large.     It  matures  during  late  winter  and  early  spring. 

OTHEE    COMMEKCIAL    VAEIETIES 

In  addition  to  the  varieties  listed  by  the  Association,  the  following 
are  also  being  grown  commercially  at  the  present  time: 

Guatemalan 

Blakeman. — Fruit  broadly  oblique,  large,  four  inches  in  length, 
and  weighing  approximately  a  pound;  surface  nearly  smooth,  dark 
green  in  color,  skin  thick  and  tough;  flesh  deep  cream  color,  of  fine 
smooth  texture;  flavor  and  quality  excellent;  seed  small  to  medium 
and  tight  in  cavity.     Season  May  to  July. 


Bulletin  365]  AVOCADO  CULTURE  IN  CALIFORNIA  623 

Originated  in  Hollywood.  The  tree  is  a  vigorous  grower,  inclined 
to  be  too  spreading  when  not  controlled  by  pruning  when  young. 
It  is  a  fair  producer.     Synonym:    Habersham.     Oil  content  2iy2%. 

Lyon. — Fruit  broadly  pyriform,  indistinctly  necked ;  length  5% 
inches,  weight  14  to  18  ounces;  surface  somewhat  rough,  rich  green  in 
color ;  skin  moderately  thick  and  tough ;  flesh  deep  cream  color,  smooth, 
free  from  fibre;  flavor  rich,  quality  very  good;  seed  broadly  conical, 
medium  size  and  tight  in  cavity.     Season  April  to  June. 

Originated  at  Hollywood.  The  tree  is  an  upright,  slender 
grower,  and  begins  bearing  when  exceedingly  young.  The  tree  is 
admirably  suited  for  inter-planting  and  for  close  plantings.  In  the 
past  it  has  been  propagated  with  difficulty  and  many  trees  have  not 
made  satisfactory  growth.  An  effort  is  being  made  to  overcome  this 
defect  and  some  success  is  reported  in  this  direction.  Oil  con- 
tent 26%%.  I.i 

Linda, — Fruit  round,  large,  weight  about  2  pounds ;  surface  rough, 
deep  purple  in  color ;  the  skin  thick  and  woody ;  flesh  yellow,  firm,  free 
from  fibre;  flavor  very  rich  and  nutty;  seed  medium  and  tight  in 
cavity.     Season  May  to  October. 

Originated  in  Guatemala;  introduced  into  California  by  E.  E. 
Knight.  This  fruit  is  one  of  the  largest  grown  in  California,  and 
ripens  over  a  long  period  of  time.  The  freeze  of  1922  indicated  that 
the  tree  should  be  planted  in  the  warmer,  protected  sections.  Oil 
content  14%. 

Queen. — Fruit  oblong-pyriform,  5y2  inches  long,  weighing  \y2 
pounds;  skin  rough,  deep  purple  in  color,  thick  and  woody;  flesh 
rich  clear  yellow,  dark  green  near  skin,  free  from  fibre ;  flavor  rich, 
quality  very  good ;  seed  very  small  and  tight  in  cavity.  Season 
March  to  October. 

The  variety  was  also  imported  by  E.  E.  Knight  from  the  highlands 
of  Guatemala.  It  is  a  vigorous  but  spreading  grower,  rather  tender, 
and  should  be  planted  only  in  the  warmest  sections.  The  tree  bears 
very  good  crops. 

Challenge. — Fruit  obliquely  spherical,  about  4  inches  in  length, 
weight  14  to  18  ounces ;  skin  thick  and  granular,  surface  rough,  color 
dark  purple;  flesh  cream  colored,  texture  smooth,  flavor  fairly  good, 
quality  medium;  seed  spherical,  very  large,  tight  in  the  cavity. 
Originated  in  Hollywood.  Tree  a  moderately  strong  grower,  prolific. 
Season  February  to  May. 

Because  of  its  low  oil  content  and  only  fair  quality  and  its  large 
seed,  this  variety  cannot  expect  to  hold  a  permanent  place  in  the 
future.  Its  attractive  appearance  and  its  prolific  bearing,  however, 
are  finding  favor  at  the  present  time  and  have  caused  an  increase  in 
its  planting. 


624  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 


MEXICAN   OR   THIN-SKINNED   VARIETIES 

In  addition  to  the  Guatemalan  varieties,  a  considerable  number 
of  thin-skinned  varieties  are  being  raised  commercially  as  well  as  for 
home  consumption.  Because  of  their  hardiness  they  enjoy  a  great 
range  of  planting,  and  because  of  their  fine  quality  and  excellent 
flavor  are  preferred  by  many  people. 

The  Tuebla,  one  of  the  varieties  recommended  by  the  Variety  Com- 
mittee of  the  Avocado  Association  and  described  elsewhere  in  this 
bulletin,  is  probably  to  be  considered  as  belonging  in  the  Mexican 
race,  although  some  have  thought  it  to  be  of  hybrid  origin.  Two 
other  of  the  more  commonly  planted  varieties  are  here  listed: 

Caliente. — Fruit  long  pyriform,  necked,  four  inches  in  length; 
weight  4  to  9  ounces,  surface  smooth,  glossy,  deep  mahogany  red  in 
color ;  skin  thin ;  flesh  cream  yellow,  smooth  with  trace  of  fibre ;  flavor 
rich,  quality  very  good ;  seed  medium,  tight  in  cavity.  Season,  October 
to  December. 

Parent  trees  located  at  Duarte,  grown  from  buds  received  from 
Mexico  by  S.  Garcia.  This  variety  apparently  stands  the  drier  atmo- 
sphere of  the  interior  sections  better  than  some  others.  It  is  a  prolific 
bearer.    The  fruit  is  particularly  attractive  in  appearance. 

Originated  at  Santa  Ana.  The  tree  is  very  hardy,  of  vigorous 
growth.     Oil  content,  27%. 

Ganier  (fig.  19). — Fruit  oval  to  obovate,  3  to  4  inches  in  length, 
weight  4  to  9  ounces;  surface  smooth,  slightly  glossy,  green  in  color; 
skin  thin;  flesh  cream  colored,  sometimes  slightly  fibrous;  flavor  rich 
and  rather  nutty ;  seed  small  to  medium,  usually  loose  in  a  fairly  large 
cavity.    Season,  October  to  December. 

Originated  at  Whittier.  The  tree  is  very  vigorous  in  growth,  hardy 
and  prolific.  The  fruit  has  the  unfortunate  capacity  for  discoloration 
and  decay  at  the  apex  before  maturity,  which  may  affect  a  considerable 
proportion  of  the  crop.    Oil  content,  25%. 

UNITED    STATES    DEPARTMENT    OF    AGRICULTURE    INTRODUCTIONS 

Twenty-three  superior  varieties  introduced  by  the  United  States 
Department  of  Agriculture  from  Guatemala  are  under  trial  in  various 
parts  of  southern  California.  These  are  now  coming  into  bearing  and 
their  behavior  under  California  conditions  is  being  watched  with  great 
interest.  They  represent  the  best  fruits  selected  by  Wilson  Popenoe 
in  his  explorations  in  that  country  extending  over  a  period  of  several 
years.  Descriptions  and  illustrations  of  these  fruits  have  already 
appeared.10 


io  The  Avocado  in  Guatemala.  Wilson  Popenoe,  U.  S.  Dept.  Agriculture. 
Bulletin  743,  Apr.  1919.  Exploring  Guatemala  for  Desirable  New  Avocados,  Wil- 
son Popenoe.     Annual  Report  California  Avocado  Association  p.  104-138,  1917. 


Bulletin  365] 


AVOCADO  CULTURE  IN  CALIFORNIA 


625 


626  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

More  recently  five  new  large-fruited  varieties  have  been  introduced 
from,  the  Chota  Valley,  Ecuador,  following"  explorations  by  Wilson 
Popenoe  in  1921.11  Trees  of  each  of  these  varieties  are  now  under  trial 
in  southern  California.  They  give  promise  of  being  valuable  addi- 
tions to  the  present  list  of  hardy  varieties. 

USES  OF  THE  FEUIT 

The  avocado  is  used  principally  as  a  salad  fruit.  As  its  general 
food  value  becomes  more  appreciated  it  will  undoubtedly  find  a  much 
larger  place  in  the  dietary  of  the  American  public.  A  discussion  of 
its  nutritive  value  is  given  in  Part  II  of  this  publication.  In  addition 
to  its  common  use  for  salads,  a  considerable  number  of  methods  of 
using  the  fruit  have  been  devised  by  housewives  and  chefs,  including 
avocado  ice  cream,  sandwich  filling  and  others.  The  reception  with 
which  these  innovations  have  been  met  is  indicative  of  the  popularity 
the  avocado  will  enjoy  once  it  is  placed  on  the  market  in  sufficient 
quantity  and  at  a  price  within  reach  of  all. 

The  demand  thus  far  has  readily  taken  care  of  all  the  fruits  pro- 
duced— good,  bad,  and  indifferent.  The  question  of  disposing  of 
second  and  third  grade  fruit  has  not  become  at  all  pressing.  There 
may  come  a  time  in  the  future  when  some  other  outlet  will  have  to 
be  developed  for  these  grades.  Preliminary  experiments  with  a  view 
to  developing  possible  by-products  have  been  undertaken  both  by  the 
Agricultural  Experiment  Station,  University  of  California,  and  by 
the  United  States  Department  of  Agriculture,  Bureau  of  Chemistry. 
The  results  obtained  so.,f ar  indicate  that  the  flesh  can  be  canned  quite 
successfully  in  a  cane  sugar  syrup.  Experiments  are  under  way  at 
the  present  time  on  the  extraction  of  avocado  oil,  and  a  very  palatable 
product  has  been  obtained.  Various  other  by-products  have  been 
attempted  but  with  little  success. 

Recent  experiments  in  dehydration  of  the  avocado  by  Cruess  and 
Christie  have  indicated  that  a  satisfactory  product  can  be  produced 
that  will  return  to  a  satisfactory  fresh  condition  when  soaked  from 
five  to  six  hours  in  water.  Many  different  tests  were  conducted.  The 
most  satisfactory  results  were  obtained  from  the  following  procedure : 
The  fruit  is  halved  and  peeled.  It  is  then  cut  into  slices  a  quarter 
of  an  inch  or  less  in  thickness.  These  slices  are  placed  on  wooden 
trays  and  subjected  to  the  fumes  of  burning  sulfur  for  fifteen  minutes. 
They  are  then  dehydrated  to  a  bone-dry  consistency  through  the  use 
of  a  temperature  of  not  less  than  140°  F.  and  not  more  than  180°  F. 


ii  "Avocados  of  the  Chota  Valley,  Ecuador,"  Wilson  Popenoe,  Annual  Keport 
California  Avocado  Association,  pp.  35-39,  1922. 


Bulletin  365]  AVOCADO  CULTURE  IN  CALIFORNIA  627 

The  drying  ratio  is  between  5  and  6  to  1.  To  avoid  rancidification 
of  the  oil,  the  product  so  prepared  is  packed  in  vacuum  sealed  jars.  On 
soaking  in  slightly  salted  water  the  fruit  returns  to  its  original  size 
and  appearance  in  five  or  six  hours.  The  flavor  is  not  quite  as  rich 
nor  quite  as  pleasing  as  that  of  the  fresh  fruit.  However,  when  cut 
in  small  pieces  and.  mixed  with  mayonnaise  dressing  it  makes  a  very 
pleasing  salad. 

YIELDS  AND  EETUENS 

The  wide  variation  in  yields  of  seedling  and  budded  trees  in  Cali- 
fornia makes  a  satisfactory  discussion  of  this  subject  difficult.  One 
point  is  certain,  that  the  practice  of  estimating  returns  on  the  basis 
of  the  large  crops  borne  by  old  seedling  trees  cannot  be  relied  upon 
with  any  measure  of  safety.  While  it  is  true  that  some  of  these  of 
both  Guatemalan  and  Mexican  types  have  produced  as  high  as  2500 
to  3000  fruits  in  a  single  season,  budded  trees  are  slower  in  growth 
and  so  far  have  not  shown  a  tendency  toward  bearing  abnormally  large 
crops.  There  has  not  been  sufficient  time  yet  for  trees  planted  under 
orchard  conditions  to  demonstrate  the  kind  of  crops  they  will  con- 
sistently produce.  At  best,  conservative  estimates  alone  are  safe. 
From  observations  made  to  date  it  would  seem  that  a  mature  bearing 
orchard  tree  of  from  ten  to  fifteen  years  of  age  should  produce  a  yearly 
average  of  one  hundred  and  fifty  pounds  of  marketable  fruit.  Esti- 
mating its  probable  value  on  a  food  basis  at  twenty  cents  a  pound,  this 
would  give  a  return  of  thirty  dollars  per  tree  or  of  $1440  gross  per 
acre  when  set  30  feet  apart,  and  $2280  gross  per  acre  when  set  24 
feet  apart.  These  figures  will  be  considered  low  by  enthusiasts,  but 
the  behavior  of  trees  to  date  does  not  warrant  more  liberal  estimates. 
No  figures  covering  the  cost  of  production  are  available,  but  this  will 
probably  not  exceed  that  of  citrus  fruits,  even  with  frost  protection 
that  should  be  provided,  for  the  avocado  is  not  as  yet  subject  to  the 
costs  of  fumigation  and  spraying  that  add  such  a  large  item  to  the 
burden  of  the  citrus  grower.  From  whatever  angle  the  question  is 
considered  avocado  culture  in  California  promises  to  be  profitable. 

OUTLOOK— PEESENT   AND   FUTUB-E 

That  the  avocado  has  come  to  stay  as  an  important  crop  in  Cali- 
fornia is  assured  beyond  a  doubt.  With  the  ever  increasing  land 
values,  especially  in  the  more  climatically  favored  portions  of  the 
state,  crops  yielding  high  gross  returns  per  acre  must  be  grown.  As 
population  becomes  more  and  more  dense  the  tonnage  of  food  produced 
per  acre  must  likewise  increase;  the  food  value  of  the  fruit  and  its 


628  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

potentially  high,  production  per  acre  are  sufficient  reasons  to  justify 
its  place  in  California  agriculture. 

Before  the  industry  can  become  stabilized,  however,  much  investi- 
gational work  will  be  required.  Hardy  varieties  which  consistently 
produce  good  crops  of  high  quality  fruit  are  yet  to  be  developed. 
The  avocado  districts  of  the  world  have  been  combed  for  varieties 
most  suited  to  California  conditions,  and  material  is  here  from  which 
to  develop  these  varieties.  Much  progress  has  already  been  made  in 
that  direction. 

So  far  no  attempts  have  been  made  to  improve  the  avocado  by 
breeding.  The  value  of  the  fruit  as  a  food  product  lies  in  its  high  oil, 
mineral,  and  protein  content.  At  present  the  oil  content  varies  from 
9%  to  32%  and  the  protein  content  from  1.3%  to  4.6%  ■  obviously 
from  a  nutritional  point  of  view  the  best  varieties  should  have  a  maxi- 
mum content  of  oil  and  protein  provided  flavor  and  quality  are  also 
maintained.  The  development  of  the  fruit  in  this  direction  lies  largely 
in  the  hands  of  the  plant  breeder.  The  effect  of  environmental  condi- 
tions on  the  quality  and  composition  of  the  fruit,  however,  must  not 
be  lost  sight  of  and  a  thorough  study  of  the  influence  of  such  factors 
still  remains  to  be  made. 

The  behavior  of  chance  seedlings  scattered  through  northern  and 
central  California  indicates  the  possibilities  of  the  development  of 
hardy  varieties  suited  to  the  climatic  conditions  of  those  sections.  The 
future  will  undoubtedly  witness  breeding  and  selection  investigations 
with  a  view  to  greatly  expanding  the  area  in  which  this  valuable  fruit 
can  be  grown.  Many  sections  in  southern  California  also  await  the 
the  development  of  hardier  varieties  than  those  now  available. 

The  area  in  which  the  avocado  may  be  grown  in  the  United  States 
is  limited.  Because  of  the  many  pests  in  the  avocado  districts  of 
Mexico,  Central  and  South  America,  fruit  from  these  regions  cannot 
be  imported  on  a  large  scale.  The  demand  for  the  fruit  at  the  present 
time  greatly  exceeds  the  supply  even  at  the  high  prices  asked. 


ACKNOWLEDGMENTS 

The  author  wishes  to  express  his  appreciation  to  Mr.  F.  0.  Popenoe, 
Mr.  Wm.  Hertrich  and  Dr.  J.  Eliot  Coit  and  other  members  of  the 
California  Avocado  Association  for  helpful  suggestions  and  especially 
to  Robert  W.  Hodgson  for  suggestions  and  helpful  criticisms  in  the 
revision  of  this  manuscript. 


Bulletin  365]  AVOCADO  CULTURE  IN  CALIFORNIA  629 


SELECTED  READING  LIST  FOR  AVOCADO  GROWERS 

1.  Manual   of   Tropical    and   Subtropical   Fruits,   Wilson   Popenoe,    1920,    The 

Macmillan  Co.,  New  York. 

2.  Annual  Reports  of  The  California  Avocado  Association,  1915-1923. 

3.  The  Avocado  in  California,  I.  J.  Condit  and  M.  E.  Jaffa,  University  of  Cali- 

fornia Agricultural  Experiment  Station  Bulletin  254,  1915. 

4.  Some  Changes  in  the  Composition  of  California  Avocados  During  Growth, 

C.  G.  Church  and  E.  M.  Chace,  U.  S.  Dept.  of  Agriculture  Bulletin  1073, 
1922. 

5.  The  Avocado  in   Guatemala,   Wilson  Popenoe,  U.   S.  Dept.   of  Agriculture 

Bulletin  743,  1919. 

6.  The  Avocado;  Its  Insect  Enemies  and  How  to  Control  Them,  G.  F.  Moznette, 

U.  S.  Dept.  Agriculture,  Farmers'  Bulletin  1261,  1922. 

7.  The  Avocado — A  Salad  Fruit  from  the  Tropics,  G.  N.  Collins,  Bulletin  77, 

Bureau  of  Plant  Industry,  1905. 

8.  The  Avocado  in  Florida,  P.  H.  Rolfs,  Bulletin  61,  Bureau  of  Plant  Industry, 

U.  S.  Dept.  of  Agriculture,  1905. 

9.  The  Trapp  Avocado,  Yearbook,  U.  S.  Dept.  of  Agriculture,  1905,  p.  508. 

10.  The  Chappelow  Avocado,  W.  S.  Taylor,  Yearbook,  U.  S.  Dept.  of  Agriculture, 

1906,  p.  363. 

11.  The  Avocado  in  Hawaii,  J.  E.,  Higgins,  C.  J.  Hunn  and  U.  S.  Holt,  Hawaii 

Agricultural  Experiment  Station  Bulletin  No.  25,  1911. 

12.  Correspondence  Course  in  Avocado  Culture,  College  of  Agriculture,  University 

of  California. 

13.  The  Avocado  in  Porto  Rico,  J.  P.  Griffiths,  Circular  72,  Dept.  of  Agriculture 

and  Labor,  Porto  Rico,  1923. 


630  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 


Part  II 
THE  NUTRITIVE  VALUE  OF  THE  AVOCADO* 

BY 

M.  E.  JAFFA  and  H.  GOSS 


The  investigation  here  reported  includes  110  analyses  representing 
68  different  varieties  of  the  avocado.  These  data  emphasize  the  value 
of  this  fruit  as  an  excellent  source  of  easily  digested  vegetable  fat. 

THE  AVERAGE  COMPOSITION  OF  FRESH  FRUITS 

A  reference  to  the  composition  of  fresh  fruit  in  general  shows 
that  the  amount  of  water  is  large,  averaging  about  83  per  cent,  and 
that  the  percentage  of  the  nutrients  indicates  that  the  main  food 
value  is  derived  from  carbohydrates.  In  nearly  all  cases  sugars  pre- 
dominate, starch  being  present  in  small  amounts  only. 

The  protein  content  of  fruits  is  low,  averaging  for  the  loquat  about 
0.2  of  one  per  cent ;  apples  and  pears,  0.4—0.5  per  cent ;  fresh  prunes, 
0.9  per  cent;  melons,  0.5  per  cent;  berries,  1-1.3  per  cent;  oranges, 
0.8-1.0  per  cent;  grapes  and  bananas,  1.2-1.5  per  cent.  The  average, 
therefore,  for  protein  for  the  fresh  fruits  enumerated  is  practically 
0.72  per  cent.    The  olive  contains  approximately  2.5  per  cent  protein. 

The  per  cents  for  the  mineral  matter  or  ash  in  fresh  fruits  are  as 
follows:  apples  and  pears,  0.3-0.4;  grapes,  0.5;  figs.  0.6;  berries,  0.6; 
oranges,  0.5  ;  melons,  0.5  ;  fresh  prunes,  0.6  ;  bananas,  1.0.  The  average 
being  0.55  per  cent,  while  the  corresponding  figure  for  meat  is  about 
1  per  cent. 

It  must  not  be  forgotten,  however,  that  while  the  amount  of  ash  is 
small,  the  percentage  of  potassium  in  the  ash  is  high.  This  is  a  very 
valuable  base-forming  element  which  is  necessary  in  the  maintenance 
of  the  normal  neutrality  of  the  blood  and  tissues.  The  importance 
of  the  mineral  matter  in  nutrition  and  the  necessity  of  carefully 
selecting  the  dietary  so  as  to  secure  a  proper  balance  between  the  base- 
forming  and  acid-forming  elements  is  becoming  more  and  more 
apparent. 


*  Credit  is  due  to  Miss  Mattie  E.  Stover  and  F.  W.  Albro  for  assistance  in 
chemical  work  incidental  to  this  investigation. 


BULLETIN  365]  AVOCADO  CULTURE  IN  CALIFORNIA  631 

Fat  is  present  in  very  small  proportions  in  fresh  fruits.  This 
constituent  is  generally  reported  as  ' '  ether  extract ' '  which  often  con- 
tains other  materials  than  the  true  fats  or  oil,  such  as  coloring  matter, 
wax  found  in  the  skin,  etc.  The  figure  reported  for  fat  in  most  fruits, 
therefore,  is  seldom  a  true  indication  of  the  content  of  this  nutrient. 

Fruits  are  important  sources  of  water-soluble  vitamins.  Par- 
ticularly is  this  true  of  the  citrus  fruits  which  are  rich  in  vitamin 
C.  The  deciduous  fruits  show  appreciable  percentages  of  B  and 
berries,  like  raspberries  and  strawberries,  show  also  a  high  content  of 
vitamin  C. 

Mature  California  grown  fruits  only  are  included  in  above  tabu- 
lation. 

COMPOSITION  OF  THE  AVOCADO 

A  survey  of  the  data  presented  in  the  accompanying  tables  shows 
the  avocado  to  differ  widely  in  many  respects  from  the  average  for 
fresh  fruits  and  proves  it  worthy  of  special  consideration.  It  might 
well  be  said  to  be  in  a  class  by  itself. 

The  tables  are  replete  with  interesting  points,  all  very  favorable 
to  the  avocado.  The  total  dry  matter  in  the  edible  portion  is,  in 
nearly  every  instance,  greater  than  that  noted  for  any  other  fresh 
fruit.  The  average  for  the  avocado,  based  on  examination  of  mature 
California  fruits  is  29.44  per  cent.  The  nearest  approach  to  this 
figure  is  found  in  the  banana  with  about  25  per  cent  dry  matter.  It 
must  be  remembered,  however,  that  while  there  may  not  be  so  much 
difference  in  the  total  amount  of  solids  of  the  two  fruits  in  question, 
there  is  a  great  difference  in  the  nature  of  the  nutrients.  Sugar  and 
starch  predominate  in  the  banana  as  against  fat  in  the  avocado. 

It  has  been  stated  that  the  protein  percent  in  all  fruits  is  low, 
averaging  less  than  one  per  cent.  It  will  be  seen  from  the  table  that 
the  minimum  figure  for  protein  in  the  avocado  is  1.14,  which  is  about 
75  per  cent  of  the  maximum,  1.5  per  cent,  noted  for  figs  and  currants. 
The  maximum,  4.39  per  cent,  credited  to  Bartley  avocado  grown  at 
Santa  Ana,  corresponds  to  the  protein  content  of  some  dried  fruits. 

It  is  of  interest  in  passing  to  note  that  a  sample  of  the  Lyon  variety 
analyzed  by  the  U.  S.  Department  of  Agriculture  also  shows  the  same 
figure,  4.39  per  cent,  as  the  maximum  for  the  protein  for  this  variety. 

In  seven  of  the  varieties  the  protein  is  in  excess  of  3  per  cent ;  in 
36  varieties  between  2  and  3  per  cent ;  while  the  average  for  83  mature 
varieties  is  2.10  per  cent. 

It  therefore  may  be  said  that  so  far  as  protein  in  fresh  fruits  is 
concerned,  the  avocado  stands  in  the  lead. 


632 


UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 


TABLE  1. — Showing  the  Composition  of  the  Avocado 


10. 
n. 

12. 
13. 

14. 
15. 

16. 
17. 
18. 
19. 
20. 
21. 
22. 
2.3. 
24. 
25. 
26. 

27. 
28. 
29. 

30. 
31. 

32. 
33. 
34. 
35. 

36. 
37. 

38. 

39. 
40. 
41. 
42. 
43. 

44. 
45. 
46. 
47. 
48. 


Variety 

Azusa 

Azusa Azusa 

Average  Azusa 

Bartley Santa  Ana. 

Beauty Orange 

Benik Duarte 

Blake Pasadena... 

Blake Whittier 

Blakeman Altadena... 

Blakeman Altadena. . . 


Weight 
of 

fruit 
Locality  grams 


Edible  Portion 


198 
169 
184 
928 
426 
518 
150 
120 
472 
454 

Average  Blakeman 463 

Brodia Orange 405 

Cabnal Duarte 459 

Cantel Duarte 351 

Cardinal Florida 587 

Caribou Duarte 464 

Caribou Duarte 486 

Average  Caribou 475 

Carmen Altadena 139 

Carton San  Fernando 169 

Carton* Riverside 108 

Challenge* Hollywood 1060 

Challenge Hollywood 669 

Champion Orange 506 

Chappelow Monrovia 181 

Chappelow Monrovia 173 

Chappelow Monrovia 104 

Chappelow Monrovia 110 

Chappelow Monrovia 1 59 

Average  Chappelow 145 

Chappelow* Altadena 80 

Condon Pasadena 143 

Condon Pasadena 150 

Average  Condon 146 

Dickey Hollywood 363 

Dickey* Nordhoff 560 

Dickinson Puente 254 

Fowler Pasadena 132 

Fuerte Yorba  Linda 315 

Fuerte Yorba  Linda 566 

Average  Fuerte 440 

Fuerte* Yorba  Linda 254 

Fuerte Altadena 270 

Fuerte Altadena 256 

Average  Fuerte 263 

Ganter Whittier 205 

Ganter* Whittier 197 

Harman* Sherman 127 

Harman* Sherman 136 

Harman* Sherman 170 

Average  Harman* 144 

Harman Sherman 235 

Harman Sherman 263 

Harman Sherman 233 

Harman Sherman 215 

Harman Sherman 192 

Average  Harman  mature 227 

Immature. 


Refuse 
per  cent 

28.30 
13.60 
21.00 
21.33 
34.07 
31.06 
32.66 
31.60 
30.30 
20.81 
25.57 
36.80 
33.11 
24.79 
19.00 
31.04 
19.80 
25.42 
31.30 
41.20 
26.06 
40.57 
17.78 
30.00 
22.43 
31.00 
36.34 
36.90 
23.30 
29.99 
30.30 
34.20 
24.00 
29.10 
30.00 
24.55 
29.99 
35.80 
25.71 
26.14 
25.92 
23.62 
26.48 
28.71 
27.59 
16.60 
26.80 
35.50 
37.90 
37.40 
36.93 
46.38 
34.70 
33.50 
34.90 
28.00 
41.61 


Water 
per  cent 

67.05 
62.69 
64.87 
77.12 
72.68 
69.98 
65.76 
68.24 
74.33 
77.72 
76.87 
80.80 
67.15 
72.04 
79.66 
82.31 
79.02 
80.66 
63.39 
70.43 
78.32 
79.61 
76.23 
74.32 
60.94 
63.58 
63.74 
58.99 
70.77 
63.61 
75.34 
69.11 
70.30 
69.70 
60.50 
81.10 
72.04 
70.33 
66.30 
68.32 
67.31 
80.88 
65.26 
65.67 
65.46 
63.86 
77.87 
75.17 
76.09 
75.42 
75.56 
71.58 
74.70 
72.05 
73.44 
72.75 
72.90 


Protein 
per  cent 

1.94 
2.91 
2.43 
4.39 
2.48 
1.97 
1.88 
1.81 
2.61 
3.15 
2.88 
1.26 
2.08 
2.43 
2.56 
1.34 
2.21 
1.77 
1.22 
2.60 
1.38 
3.43 
2.81 
2.59 
1.40 
2.63 
2.19 
2.79 
2.25 
2.25 
2.30 
2.50 
1.31 
1.91 
2.20 
2.01 
1.56 
1.60 
1.42 
1.36 
1.39 
1.04 
1.40 
1.51 
1.46 
2.25 
2.13 
1.69 
1.24 
1.47 
1.47 
2.50 
1.60 
1.43 
1.14 
1.16 
1.57 


Fat 
per  cent 

21.06 

26.44 

23.75 

13.35 

15.26 

22.02 

25.50 

21.65 

17.27 

15.43 

16.35 

10.88 

23.71 

19.00 

10.70 

10.33 

12.00 

11.17 

26.38 

19.50 

12.71 

13.14 

16.37 

16.54 

29.10 

24.43 

22.81 

27.66 

20.28 

24.85 

14.66 

21.00 

23.55 

22.23 

27.11 

11.81 

20.36 

21.20 

25.32 

24.23 

24.77 

11.61 

28.68 

26.60 

27.64 

25.60 

16.48 

15.25 

15.34 

16.26. 

15.62 

19.33 

18.30 

21.51 

18.68 

19.18 

19.40 


Carbo- 
hydrates 
per  cent 

8.59 
6.15 
7.37 
3.74 
8.22 
4.42 
5.52 
8.18 
4.94 
2.59 
3.76 
6.30 
5.69 
4.90 
6.48 
4.60 
5.43 
5.02 
7.46 
6.29 
6.60 
2.62 
3.05 
5.31 
6.85 
8.06 
10.00 
9.33 
5.13 
7.88 
6.80 
6.73 
3.62 
5.17 
8.76 
3.75 
4.69 
5.61 
5.68 
4.82 
5.25 
5.53 
3.22 
4.62 
3.92 
6.58 
2.48 
7.00 
6.65 
5.86 
6.50 
5.32 
4.60 
4.24 
5.17 
5.86 
5.03 


Ash 
per  cent 

1.36 
1.81 
1.58 
1.40 
1.36 
1.61 
1.34 
1.12 
0.85 
1.11 
0.98 
0.76 
1.37 
1.59 
0.60 
1.42 
1.34 
1.38 
1.55 
1.18 
0.99 
1.20 
1.54 
1.24 
1.71 
1.30 
1.26 
1.23 
1.57 
1.41 
0.90 
0.66 
1.22 
0.94 
1.43 
1.33 
1.35 
1.26 
1.28 
1.27 
1.28 
0.94 
1.44 
1.60 
1.52 
1.71 
1.04 
0.89 
0.68 
0.99 
0.85 
1.27 
0.80 
0.77 
1.57 
1.05 
1.10 


Bulletin  365] 


AVOCADO  CULTURE  IN   CALIFORNIA 


633 


TABLE   1.— (Continued) 


Variety 


Locality 


89. 
90. 

91. 

92. 
93. 
94. 


I.  X.  L  * Duarte 

I.  X.  L Duarte 

Kist Yorba  Linda.. 

Kist Yorba  Linda.. 

Average  Kist 

Lamat Duarte 

Lambert Hollywood 

Lyon Hollywood 

Lyon La  Habra 

Mattern Unknown 

Mayapan Duarte 

Mayapan Duarte 


Weight 

of 

fruit 

grams 

705 
800 
456 
478 
467 
332 
285 
453 
453 
92 
397 
449 


Edible  Portion 


Average  Mayapan 423 

Meserve Puente ?..:.  331 

Miller Hollywood 184 

Miller Pasadena 275 

Monrovia Altadena 166 

Nimlich Duarte 860 

Northrup Santa  Ana 164 

Pankay Duarte 385 

Pankay Duarte 310 

Average  Pankay 347 

Pomona Sacramento 79 

Popenoe  101 Altadena 327 

Popenoe  101 Altadena 375 

Average  Popenoe  101 346 

Puebla* Altadena 168 

Puebla Altadena 280 

Puebla Altadena 158 

Average  Puebla  mature 219 

Purdy Whittier 168 

Purple  Prolific  ....Orange 219 

Queen Unknown 663 

Queretaro Yorba  Linda 217 

Queretaro Altadena 164 

Rhoad Orange 395 

Rita* Orange 321 

Royal Hollywood 600 

Royal  Purple San  Diego 200 

Senor Orange 528 

Sharpless* Santa  Ana 471 

Sharpless* Santa  Ana 555 

Average  Sharpless* 513 

Sharpless Santa  Ana 594 

Sharpless Santa  Ana 536 

Average  Sharpless 565 

Sinaloa Whittier 616 

Spinks Duarte 388 

Spinks Duarte 877 

Average  Spinks 633 

Surprise Hollywood 538 

Taft Orange 626 

Taft* Orange 417 

Taft* Orange 296 

Average  Taft* 356 

Immature. 


Refuse 
per  cent 

31.60 
23.00 
31.35 
28.20 
29.77 
30.42 
33.40 


26.50 
44.00 
37.28 
28.06 
32.67 
40.00 
35.80 
40.00 
37.00 
24.42 
34.70 
41.30 
46.12 
43.76 
43.00 
23.82 
29.34 
26.58 
34.00 
27.50 
36.00 
31.75 
32.10 
45.90 
29.15 
37.80 
36.60 
37.00 
42.68 
26.33 
26.00 
21.00 
21.23 
22.50 
21.86 
23.10 
24.10 
23.65 
23.40 
31.50 
20.30 
25.90 
26.00 
29.00 
25.00 
27.00 
26.00 


Water 
per  cent 

84.27 
78.12 
76.84 
74.71 
75.78 
77.32 
76.52 
75.78 
74.80 
61.55 
68.33 
70.26 
69.29 
74.66 
66.60 
63.68 
64.18 
78.55 
66.31 
73.15 
71.03 
72.09 
61.84 
58.71 
60.78 
59.74 
80.59 
69.47 
67.53 
68.50 
60.28 
69.30 
73.80 
71.46 
71.46 
82.46 
71.05 
76.34 
72.96 
74.70 
76.73 
75.33 
76.03 
71.21 
72.63 
71.92 
73.55 
76.22 
75.72 
75.97 
82.51 
72.53 
76.11 
77.25 
76.68 


Protein 
per  cent 

2.12 
2.17 
1.51 
2.41 
1.96 
1.42 
2.86 
2.48 
2.76 
2.20 
1.77 
2.25 
2.01 
2.19 
3.70 
3.36 
2.09 
1.53 
2.36 
1.58 
1.64 
1.61 
3.50 
2.39 
1.82 
1.65 
1.76 
1.66 
1.83 
1.74 
1.14 
1.67 
2.21 
2.85 
2.34 
1.19 
1.57 
1.39 
1.72 
1.69 
2.15 
3.06 
2.60 
1.70 
1.27 
1.48 
2.67 
1.50 
2.10 
1.80 
1.90 
2.66 
2.30 
3.44 
2.87 


Fat 
per  cent 

7.50 
13.47 
12.16 
14.92 
13.54 
14.29 
14.31 
16.31 
15.58 
25.70 
22.83 
21.80 
22.32 
17.01 
23.70 
27.45 
25.34 
13.93 
23.00 
14.56 
16.30 
15.43 
25.36 
31.59 
29.78 
30.68 
11.32 
20.94 
26.14 
23.54 
31.60 
19.93 
16.35 
17.45 
18.21 

9.78 
14.13 
15.61 
19.39 
17.03 
15.73 
15.87 
15.80 
20.54 
18.77 
19.65 
16.43 
14.83 
16.01 
15.42 

9.96 
18.54 
14.67 
12.59 
13.63 


Carbo- 
hydrates 
per  cent 

4.70 
4.74 
8.13 
6.49 
7.31 
5.57 
5.40 
4.38 
6.01 
8.94 
5.59 
4.13 
2.86 
4.78 
4.51 
4.18 
6.73 
4.83 
7.12 
9.10 
9.61 
9.36 
7.36 
5.65 
5.92 
5.78 
5.22 
6.65 
3.16 
4.91 
5.49 
8.27 
6.01 
6.79 
6.56 
6.03 
12.25 
5.97 
4.84 
5.45 
3.69 
4.52 
4.11 
5.43 
6.39 
5.91 
5.57 
5.96 
4.74 
5.35 
4.86 
5.16 
6.00 
4.91 
5.45 


Ash 
per  cent 

1.41 

1.50 

1.36 

1.47 

1.41 

1.40 

0.91 

1.05 

0.85 

1.61 

1.48 

1.56 

1.52 

1.36 

1.49 

1 

1 

1 

1 

1 

1.42 

1.51 

1.94 

1.66 

1.70 

1.68 

1.11 

1.28 

1.34 

1.31 

1.49 

0.83 

1.63 

1.45 

1.43 

0.54 

1.00 

0.69 

1.09 

1.13 

1.70 

1.22 

1.16 

1.12 

0.94 

1.03 

1.78 

1.49 

1.43 

1.46 

0.77 

1.11 

0.92 

1.81 

1.37 


634 


UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 


TABLE   1.— (Continued) 


Variety 


Locality 


Weight 

of 

fruit 

grams 

123 
638 
277 
174 
259 
450 
123 
102.  White Santa  Barbara....       162 


95.  Topa  Topa NordhofT.... 

96.  Trapp Florida 

97.  Ultimate Orange 

98.  Walker Sherman.... 

99.  Wagner Hollywood. 

100.  Dr.  Weldon Duarte 

101.  W.  I.  G Altadena 


Maximum. 
Minimum.. 
Average 


No.  of 

Analyses 

83 

83 

83 


Edible  Portion 


Carbo- 
Refuse      Water     Protein       Fat      hydrates       Ash 
per  cent  per  cent  per  cent  per  cent  per  cent  per  cent 


Weight 

of 

fruit 

grams 

928 

79 

347 


27.70 
28.50 
37.40 
37.10 
47.00 
41.00 
28.50 


75.00 
78.66 
75.01 
68.66 
74.84 
63.75 
60.00 


2.30 
1.61 
1.57 
3.15 

2.77 
2.57 
2.63 


15.48 
9.80 
14.51 
18.71 
16.03 
24.29 
26.73 


6.14 
9.08 
4.88 
7.55 
5.05 
7.79 
9.08 


35.00       77.06       1.74 


14.64       5.49 


1.08 
0.85 
1.03 
1.93 
1.30 
1.60 
1.56 
1.07 


Carbo- 

Refuse     Water     Protein        Fat      hydrates      Ash 

per  cent  per  cent  per  cent   per  cent  per  cent  per  cent 

47.00       82.31       4.39         31.60       10.00         1.94 

13.60       58.71        1.14  9.78       2.59  0.54 

32.11        70.56       2.10         20.06       5.95  1.32 


Mature  California  grown  fruits  only  are  included  in  above  tabulation. 


Partial  Analyses 


Variety 


Locality 


Weight 

of  fruit         Refuse  Water  Fat 

grams         per  cent        per  cent     per  cent 


1.  Atlixco Yorba  Linda.. 

2.  Atlixco Yorba  Linda.. 

Average  Atlixco 

3.  Goldie San  Diego 

4.  Knight Yorba  Linda.. 

5.  Linda Unknown 

6.  Snell Sierra  Madre. 

7.  Tahiti San  Diego 

8.  Whittier Whittier 


352 

26.52 

63.70 

28.80 

532 

26.86 

63.10 

26.90 

442 

26.69 

63.40 

27.95 

165 

35.50 

56.50 

26.67 

570 

26.95 

71.03 

23.31 

890 

20.23 

82.66 

7.48 

306 

29.00 

55.00 

32.70 

256 

19.50 

50.60 

23.20 

687 

23.00 

75.20 

21.20 

The  carbohydrate  content  of  the  avocado  is  low  as  compared  with 
this  constituent  in  fresh  fruits.  The  average  for  the  83  mature 
varieties  is  5.95  per  cent,  with  a  maximum  of  10  per  cent  and  a 
minimum  of  2.59  per  cent. 

The  figures  quoted  in  the  table  for  carbohydrates  include  crude 
fiber  which  was  not  determined  in  every  case.  Analyses  of  a  number 
of  samples  have  shown,  however,  that  this  ingredient  would  average 
about  1.5  per  cent,  which  compares  very  favorably  with  the  content 
of  crude  fiber  in  other  fresh  fruits. 

It  is  of  decided  interest  to  note  that  the  percentage  of  mineral 
matter  in  the  avocado  is  much  higher  than  that  recorded  for  any  other 
fresh  fruit.  The  minimum  0.54  per  cent,  reported  for  the  Rhoad 
variety,  equals  approximately  the  average  for  most  of  our  fresh  fruits, 
while  the  average  for  the  avocado,  1.32  per  cent,  shows  that  it  contains 
twice  as  much  mineral  matter  as  that  yielded  by  any  other  fruit. 


Bulletin  365]  AVOCADO  CULTURE  IN  CALIFORNIA  635 

The  following  analysis  of  the  ash  of  the  avocado  shows  that,  like 
other  fruit,  the  avocado  yields  an  excess  of  the  base-forming  elements : 

Silica 0.50 

Phosphoric  acid   17.40 

Lime    4.72 

Magnesia    5.30 

Iron   1.51 

Aluminum     2.58 

Manganese    Trace 

Sulfuric   Acid 11  °4 

Chlorin    14.36 

Potash  26.23 

Soda    18.55 

101.89 
Oxygen  equivalent  to  chlorin  2.09 

99.80 

Nearly  one-half  of  the  ash  consists  of  soda  and  potash,  the  latter 
predominating.  Magnesia  and  lime  occur  in  comparatively  small 
amounts,  about  5  per  cent  each;  the  phosphoric  acid  averaging  about 

17.5  per  cent,  with  1.5  per  cent  of  iron. 

The  foregoing  discussion  clearly  indicates  that  so  far  as  protein 
and  ash  in  fresh  fruits  are  concerned,  the  avocado  stands  at  the  head 
of  the  list,  and,  with  reference  to  the  carbohydrates,  contains  on  an 
average  fully  50  per  cent  of  that  found  in  many  fresh  fruits.  These 
facts  alone  would  warrant  due  consideration  of  the  value  of  the 
avocado  as  a  fresh  fruit. 

The  chief  value  of  the  avocado  as  food,  however,  is  due  to  its  high 
content  of  fat.  This  varies,  as  shown  by  the  analyses,  from  a  minimum 
of  9.78  per  cent  to  a  maximum  of  31.6  per  cent,  with  an  average  of 

20.6  per  cent. 

Reviewing  the  analytical  data,  it  will  be  seen  that  15  varieties 
show  more  than  25  per  cent  fat  and  14  other  varieties  an  excess  of 
20  per  cent.  The  only  fruit  comparable  with  the  avocado  in  this 
respect  is  the  olive.  In  this  connection,  it  is  of  interest  to  note  the 
comparison  as  shown  in  the  following  table,  of  the  fat  percentages  of 
the  edible  portion  of  ten  varieties  of  the  avocado  containing  25  per 
cent  or  more  of  fat,  with  ten  varieties  of  the  olive. 


636 


UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 


TABLE  2. — Showing  Percentage  of  Fat  or  Oil  in  the  Avacado  and  Olive 


Avocado — Edible  Portion 

Original  Material     Water-Free 

Water 
Variety  per  ct. 

Purdy  60.28 

Popenoe  59.74 

Chappelow    60.94 

Fuerte  65.26 

Miller 63.68 

Dickey  60.50 

Azusa 62.69 

Carmen   63.39 

Ganter  63.86 

Blake  65.76 


Fat 

Fat 

per  ct. 

per  ct. 

31.60 

79.70 

30.68 

76.20 

29.10 

74.40 

28.68 

82.50 

27.45 

75.60 

27.11 

68.70 

26.44 

70.90 

26.38 

72.10 

25.60 

70.80 

25.50 

74.50 

Olive — Edible  Portion 

Original  Material 

Oil 
Variety  per  ct. 

Corregiolo    27.68 

Nigerina  26.16 

Nevadillo   Blanco....  22.92 

Mission 22.51 

Rubra   22.01 

Pendulina    21.36 

Redding  Picholine....  20.83 

Macrocarpa   20.41 

Manzanillo    19.73 

Columbella  19.54 


The  figures  in  table  2  indicate  that  the  avocado  ranks  higher  in 
fat  or  oil  than  the  average  or  commonly  used  olive.  The  olive  also 
has  the  disadvantage  of  requiring  special  treatment  before  it  is  ready 
for  consumption  and  should  really  rank  as  a  processed  fruit  rather 
than  a  fresh  one.  The  data  in  the  table  show  that,  when  considering 
the  dry  matter  only,  the  Purdy  has  the  highest  per  centage  of  fat. 
In  the  original  condition,  the  Blake  and  the  Chappelow  differ  in  fat  by 
nearly  4  per  cent,  which  difference  is  practically  eliminated  when  com- 
parison is  made  on  a  water-free  basis,  which  is  the  only  true  way  to 
compare  the  nutritive  value  of  fruits. 

CALORIC  VALUE 

While  it  is  true  that  the  real  value  of  any  food  is  not  always  rep- 
resented by  the  heat  units  or  calories,  at  the  same  time,  the  total  food 
value  is  so  indicated.  This  difference  between  the  real  food  value 
and  the  total  food  value  is  not  always  properly  understood.  For 
instance,  the  energy  value  of  a  pound  of  sugar  is  1820  calories,  while 
the  corresponding  value  for  lean  meat  is  less  than  1000  calories.  Yet 
we  would  hardly  say  that  the  real  value  of  a  pound  of  sugar  was  1.8 
times  that  of  a  pound  of  lean  meat,  if  the  question  of  growth  were 
under  consideration.  When,  however,  the  matter  of  energy  is  being 
discussed  the  case  is  entirely  different,  and  the  value  of  a  food  as  a 
source  of  energy  varies  directly  with  its  caloric  value. 

The  energy  values  of  the  edible  portion  of  the  commonly  used 
fresh  fruits  are  low,  ranging  from  a  minimum  of  175  calories  to  a 
possible  maximum  of  400  calories  per  pound. 

An  inspection  of  table  3  shows  that  the  avocado  has  a  far  higher 
value  in  this  respect,  the  average  for  twenty  varieties,  being  1056  per 
pound,  or  more  than  twice  the  maximum   (400  calories)   noted  for 


BULLETIN  365]  AVOCADO  CULTURE  IN  CALIFORNIA  637 

other  fresh  fruits.  The  minimum,  783  calories,  approaches  very 
closely  to  this  figure.  The  maximum,  1376  calories  per  pound,  cor- 
responds to  that  noted  for  some  varieties  of  dried  fruits.  It  is  prac- 
tically 75  per  cent  of  the  fuel  value  of  the  cereals  and  far  in  excess 
of  the  fuel  value  of  lean  meat. 

TABLE  3. — Showing  the  Energy  Value  of  the  Avocado 

Energy  value  Energy  value 

No.  and  per  pound  No.  and  per  pound 

variety  calories  variety  calories 

1.  Azusa    1,235  12.  Mayapan  992 

2.  Blake  1,083  13.  Miller    1,159 

3.  Blakeman  783  14.  Northrup  1,101 

4.  Cabnal  1,100  15.  Pomona  1,223 

5.  Chappelow    1,184  16.  Popenoe    1,376 

6.  Dickey     1,293  17.  Puebla    1,026 

7.  Dickinson   958  18.  Queen  812 

8.  Fuerte   1,187  19.  Sharpless    928 

9.  Ganter  1,195  20.  Sinaloa    814 


10.  Harman  904  

11.  Lyon    785  Average  1,056 

DIGESTIBILITY 

Digestion  experiments  conducted  by  Mattill12  have  shown  that  the 
digestion  coefficient  for  avocado  fat  for  man  is  93.8,  which  is  identical 
with  the  average  obtained  by  Dr.  Langworthy  and  Holmes  in  connec- 
tion with  the  digestibility  of  butter  fat  by  man.  In  other  words,  the 
digestibility  of  avocado  fat  is  on  a  par  with  butter  fat. 

There  have,  however,  been  no  metabolism  experiments  carried  on 
in  connection  with  the  protein  and  carbohydrates  of  the  avocado,  yet 
it  is  only  fair  to  assume  that  this  fruit  is  as  easily  digested  as  many 
others  whose  coefficients  have  been  determined.  Such  data  clearly 
prove  that  the  fruits  are  quite  thoroughly  digested.  The  availability 
of  the  fats  and  mineral  matter  are  fully  equal  to  that  obtained  for  the 
mixed  diet;  and  the  digestion  coefficients  of  the  carbohydrates  com- 
pare very  favorably  with  the  corresponding  figures  for  other  foods, 
but  the  availability  of  the  protein  is  appreciably  lower. 

VITAMINS 

Dr.  Santos13  has  shown  that  the  avocado  is  an  excellent  source  of 
vitamin  B  or  the  antineuritic  vitamin.  He  found  that  one-half  gram 
of  the  avocado  as  a  daily  supplement  to  the  standard  vitamin  B  free 
diet,  caused  a  recovery  in  the  weight  of  rats  which  had  been  declining 
because  of  lack  of  this  accessory  food  factor. 

Studies  are  now  in  progress  by  the  Nutrition  Division  for  the 

purpose  of  ascertaining  the  content  of  vitamin  C  in  the  avocado.    This 

12  California  Avocado  Association,  Annual  Report,  1916. 
is  Amer.  Jour.  Physiol.  LIX,  1922,  p.  310. 


638  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

fruit  is  eaten  raw  and  therefore  if  it  proves  to  be  high  in  vitamin  0, 
its  nutritional  value  will  be  greatly  enhanced.  There  are  many  fruits 
and  foods  which  contain  appreciable  amounts  of  vitamin  C  in  the  raw 
state  but  which  have  to  be  processed  or  cooked  before  ready  for  con- 
sumption, resulting  in  a  great  lowering  of  the  potency  of  the  anti- 
scorbutic vitamin.  In  some  instances,  cooking  or  processing  is  entirely 
destructive  to  this  accessory  food  factor. 

DIETETIC   VALUE 

The  dietetic  value  of  fruit,  aside  from  the  actual  nutrients  which 
it  contains,  lies  in  its  succulency,  its  minerals,  its  vitamins,  and  its 
organic  acids.  If  gauged  by  its  nutritive  value  alone,  fruit  would 
seem  to  be  an  expensive  form  of  nourishment,  but  when  its  hygienic 
qualities  are  considered  its  money  value  to  the  consumer  is  difficult 
to  estimate.  Some  fruits  carry  more  nourishment  with  their  hygienic 
properties  than  others.  Some  contain  minerals  which  are  more  valu- 
able to  the  system  or  less  commonly  distributed  than  others.  Again, 
there  are  the  citrus  fruits  which  are  rich  in  vitamin  C.  Therefore, 
while  there  are  general  properties  which  are  common  to  all  fruits,  each 
has  special  properties  which  justify  individual  consideration. 

While  the  special  dietetic  value  of  a  food  can  not  always  be  fore- 
cast by  the  chemical  analysis,  it  is  certainly  permissible  to  suggest 
the  possibilities  which  are  indicated  by  the  results  of  such  investiga- 
tion. It  is  always  necessary  that  such  theory  be  confirmed  by  clinical 
experience. 

Judging  from  its  composition,  the  avocado  should  perhaps  prove 
to  have  laxative  qualities  of  a  peculiar  or  individual  type,  possessing 
as  it  does  the  combination  of  the  usual  " fruit  principles,"  and  that 
of  fat  or  oil.  The  laxative  properties  of  most  fruits  depend  upon  the 
stimulating  effects  of  the  fiber  upon  the  wall  of  the  intestine  and 
partly  upon  the  organic  acids  and  minerals.  Oil  has  a  tendency  to 
soothe  and  to  lubricate  the  intestine  even  while  it  acts  as  a  mild  laxa- 
tive. The  avocado  is  a  natural  combination  of  these  two  types  of 
foods — as  if  fruit  and  olive  oil  had  been  chemically  combined  by 
nature.  Whether  or  not  there  is  any  special  advantage  in  this  natural 
combination  over  that  made  by  a  proper  selection  of  foods  remains 
to  be  proved.  There  are  no  clinical  data  on  the  subject,  but  future 
experimental  work  may  furnish  some  interesting  results. 

The  fact  that  the  native  Cubans  prefer  this  fruit  to  any  other  of 
their  abundant  supply  may  be  due  to  its  flavor  alone,  but  it  is  more 
than  likely  that  the  preference  has  a  deeper  foundation  and  that  it 
is  the  result  of  generations  of  experience  or  knowledge  of  its  beneficial 
effects. 


